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\title{THE `GRAVITATIONAL LENSING' BIBLIOGRAPHY}
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\author{A.~Pospieszalska-Surdej$^{1}$, J.~Surdej$^{1}$ and Ph.~V{\'e}ron$^{2}$\\
\vspace{1cm}\\
\normalsize $^1$Institut d'Astrophysique, Universit{\'e} de Li{\`e}ge, Belgique\\
\normalsize $^2$Observatoire de Haute-Provence, Saint-Michel l'Observatoire, 
France\\}
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{\noindent\small{\bf Abstract:} 
We present a non exhaustive bibliography on ``Gravitational Lensing'' (GL), 
totalizing nearly 2000 titles. It also includes recent abstracts
of papers dealing with gravitational lensing and submitted to 
astro-ph@babbage.sissa.it. \\

The GL bibliography is accessible via WWW (take a look at URL 

http://vela.astro.ulg.ac.be/grav{\_}lens/grav{\_}lens.html). \\

We are aware that the present compilation is not complete, not always 
uniform and that there are still errors, typos, etc. We would appreciate 
very much if you could communicate to us (via E-mail: 
`asurdej@astro.ulg.ac.be' or `surdej@astro.ulg.ac.be') missing or new titles 
(published or accepted for publication), errors, changes and suggestions. \\

It would also be nice for us to receive in the future your preprints or 
reprints related to `Gravitational Lensing' studies. Please send your
material to: A. Surdej or J. Surdej, Institut d'Astrophysique, Avenue de 
Cointe, 5, B-4000 Li{\`e}ge, Belgique }

\newpage

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\beginrefer

\refer [ABR93.1]  Abraham, R.G., Crawford, C.S., Marrifield, M.R., Hutchings, J.B., McHardy, I.M.:  1993, {\sl  Astrophys. J.\/} {\bf 415}, 101, ``Is the BL Lac AO 0235+164 being lensed by its intervening MgII absorber?'' 

\refer [ABR91.1]  Abraham, R.G., McHardy, I.M., Crawford, C.S.:  1991, {\sl  Monthly Notices Roy. Astron. Soc.\/} {\bf  252},  482, ``Optical imaging of BL Lac host galaxies'' 

\refer [ADA89.1]  Adam, G., Bacon, R., Court{\`e}s, G., Georgelin, Y., Monnet, G., P{\'e}contal, E.:  1989, {\sl  Astron. Astrophys.\/} {\bf  208},  L15, ``Observations of the Einstein cross 2237+030 with the TIGER Integral Field Spectrograph'' 

\refer [ADA79.1]  Adams, M.T., Boroson, T.A.:  1979, {\sl  Nature\/} {\bf  282},  183, ``Direct imaging of the twin QSOs 0957+561 A and B: the gravitational lens interpretation'' 

\refer [AFR82.1]  Afraimovich, E.L.:  1982, {\sl  Astron. Astrophys.\/} {\bf  105},  L5, ``Spectral analysis of interfering delay signals as applied to detection of gravitational lenses'' 

\refer [AFR82.2]  Afraimovich, E.L.:  1982, {\sl  Soviet Astron. Letters\/} {\bf  8},  70, ``Spectrum analysis of interfering delayed signals as a tool for detecting gravitational lenses'' 

\refer [AGO96.1]  Agol, E.:  1996, {\sl  Monthly Notices Roy. Astron. Soc.\/} {\bf  279}, 571, ``Polarization during binary microlensing''

\refer [ALA95.1]  Alard, C., Mao, S., Guibert, J.:  1995, {\sl Astron. Astrophys.\/} {\bf  300},  L17, ``Object DUO2: a new binary lens candidate?''

\refer [ALC82.1]  Alcock, C.:  1982, {\sl  Nature\/} {\bf  295},  284, ``Gravitational lens'' 

\refer [ALC95.3]  Alcock, C., Allsman, R.A., Alves, D., Axelrod, T.S., Bennett, D.P., Cook, K.H. et al. (The MACHO Collaboration):  1995, {\sl Astrophys. J.,\/} {\bf  454},  L125, ``First observation of parallax in a gravitational microlensing event''

\refer [ALC96.1]  Alcock, C., Allsman, R.A., Alves, D., Axelrod, T.S., Becker, A. et al.:  1996, {\sl Astrophys. J.\/} {\bf  463},  L63,  ``Real-time detection and multisite observations of gravitational microlensing''

\refer [ALC96.3]  Alcock, C., Allsman, R.A., Alves, D., Axelrod, T.S., Becker, A. et al.:  1996, {\sl Astrophys. J.\/} {\bf  471},  774, ``The MACHO Project: Limits on Planetary Mass Dark Matter in the Galactic Halo from Gravitational Microlensing''

\refer [ALC95.1]  Alcock, C., Allsman, R.A, Axelrod, T.S, Bennett, D.P, Cook, K.H. et al. (MACHO Collaboration):  1995, {\sl Phys. Rev. Let.\/} {\bf  74},  2867, ``Experimental limits on the dark matter halo of the galaxy from gravitational microlensing''

\refer [ALC95.2]  Alcock, C., Allsman, R.A., Axelrod, T.S., Bennett, D.P., Cook, K.H. et al.:  1995, {\sl Astrophys. J.\/} {\bf  445},  133, ``Probable gravitational microlensing towards the galactic bulge''

\refer [ALC95.5]  Alcock, C., Allsman, R., Axelrod, T., Bennett, D., Cook, K.H., Evans, N.W. et al.:  1995, {\sl Astrophys. J.\/} {\bf  449},  28, ``Theory of exploring the dark halo with microlensing.I. Power-law models''

\refer [ALC96.2]  Alcock, C., Allsman, R., Axelrod, T., Bennett, D., Cook, K.H. et al. (The MACHO Collaboration):  1996, {\sl Astrophys. J.\/} {\bf  461}, 84, ``The MACHO project first year LMC results: The microlensing rate and the nature of the galactic dark halo''

\refer [ALC85.1]  Alcock, C., Anderson, N.:  1985, {\sl  Astrophys. J.\/} {\bf  291},  L29, ``On the use of measured time delays in gravitational lenses to determine  the Hubble constant'' 

\refer [ALC86.1]  Alcock, C., Anderson, N.:  1986, {\sl  Astrophys. J.\/} {\bf  302},  43, ``On the distance measure for gravitational lenses'' 

\refer [ALC93.1]  Alcock, C., Akerlof, C.W., Allsman, R.A., Axelrod, T.S., Bennett, D.P. et al.:  1993, {\sl Nature\/} {\bf 365},  621, ``Possible gravitational microlensing of a star in the Large Magellanic Cloud'' 

\refer [ALE95.1]  Alexander, T.:  1995,  {\sl Monthly Notices Roy. Astron. Soc.\/} {\bf  274},  909, ``The signature of microlensing in QSO variability-redshift correlations''

\refer [ALL89.1]  Allen, B.:  1989, {\sl  Phys. Rev. Let.\/} {\bf  63},  2017, ``Gravitational lenses as long-baseline gravitational-wave detectors'' 

\refer [ALL96.1]  Allen, S.W., Fabian, A.C., Kneib, J.P.:  1996,  {\sl  Monthly Notices Roy. Astron. Soc.\/} {\bf 279}, 615, ``A combined X-ray and gravitational lensing study of the massive cooling-flow cluster PKS0745-191''

\refer [ALT91.1]  Altieri, B., Giraud, E.:  1991, {\sl  The Messenger\/} {\bf  63},  65, ``Microlensing in the "Cloverleaf" quasar H1413+117?'' 

\refer [AND86.1]  Anderson, N., Alcock, C.:  1986, {\sl  Astrophys. J.\/} {\bf  300},  56, ``The effect of clustering of galaxies on the statistics of gravitational lenses'' 

\refer [ANG90.1]  Angonin, M.-C., Remy, M., Surdej, J., Vanderriest, C.:  1990, {\sl  Astron. Astrophys.\/} {\bf  233},  L5, ``First spectroscopic evidence of microlensing on a BAL quasar? The case of H 1413+117'' 

\refer [ANG94.1]  Angonin-Willaime, M.-C., Soucail, G., Vanderriest, C.:  1994, {\sl Astron. Astrophys.\/} {\bf  291},  411, ``Gravitational lensing of Q0957+561: a study of the cluster at z=0.355''

\refer [ANG94.2]  Angonin-Willaime, M.-C., Vanderriest, C., Hammer, F., Magain, P.:  1994, {\sl  Astron. Astrophys.\/}, {\bf 281}, 388, ``Further observational evidences that MG J0414+0534 is a gravitational lens mirage'' (Erratum: 1994, {\sl  Astron. Astrophys.\/} {\bf  292}, 722)

\refer [ANN92.1]  Annis, J.T.:  1992, {\sl  Astrophys. J.\/} {\bf  391},  L17, ``The unusual K-band characteristics of the gravitational lens system MG1131+0456'' 

\refer [ANN93.2]  Annis, J., Gioia, I., Luppino, G.:  1993, {\sl  ASP Conf. Ser.\/} {\bf 51},  432, {\sl "Observationnal Cosmology", 1992, Milano\/} ``The Hawaii Arc Survey: Survey for gravitational lensing in x-ray selected clusters of galaxies'' 

\refer [ANN93.1]  Annis, J.T., Luppino, G.A.:  1993, {\sl  Astrophys. J.\/} {\bf  407},  L69, ``Infrared Imaging of MG0414+0534: The red gravitational lens systems as lensed radio galaxies'' 

\refer [ANS95.2]  Ansari, R., Cavalier, F., Couchot, F., Moniez, M., Perdereau, O. et al.:  1995, {\sl  Astron. Astrophys.\/} {\bf  299}, 21, `` Variability of the EROS no2. microlensing candidate''

\refer [ANS96.1]  Ansari, R., Cavalier, F., Moniez, M., Aubourg, E., Bareyre, P. et al.:  1996, {\sl Astron. Astrophys.\/} {\bf  314},  94, ``Observational limits on the contribution of substellar and stellar objects to the galactic halo''

\refer [ARN88.2]  Arnaud, J., Hammer, F., Jones, J., Le F{\`e}vre, O.:  1988, {\sl Astron. Astrophys.\/} {\bf 206}, L5, ``Detection of a galaxy near the line of sight toward the QSO 1209+107''

\refer [ARN94.1]  Arnaud, M. et al.:  1994, {\sl  Experimental Astronomy\/} {\bf  4},  265, ``A 20cm**2 CCD mosaic camera for a dark matter search. PartI: mechanics, optics and cryogeny''

\refer [ARN94.2]  Arnaud, M. et al.:  1994, {\sl  Experimental Astronomy\/} {\bf  4},  279, ``A 20cm**2 CCD mosaic camera for a dark matter search. PartII: electronics, data acquisition and performence''

\refer [ARP90.1]  Arp, H.:  1990, {\sl  Astron. Astrophys.\/} {\bf  229},  93, ``Quasar numbers as a function of apparent magnitude: gravitational lensing or quasars associated with nearby galaxies?'' 

\refer [ARP84.1]  Arp, H., Gavazzi, G.:  1984, {\sl  Astron. Astrophys.\/} {\bf  139},  240, ``A third quasar close to NGC3842'' 

\refer [ARP80.1]  Arp, H., Hazard, C.:  1980, {\sl  Astrophys. J.\/} {\bf  240},  726, ``Peculiar configurations of quasars in two adjacent areas of the sky''

\refer [ARP79.1]  Arp, H., Sargent, W.L.W., Willis, A.G., Oosterbaan, C.E.:  1979, {\sl  Astrophys. J.\/} {\bf  230},  68, ``An eruptive BL Lacertae object with a high redshift, 0846+51W1'' 

\refer [ARP92.1]  Arp, H., Crane, P.: 1992, {\sl  Phys. Let. A\/} {\bf  168},  6, ``Testing the gravitational lens hypothesis in G2237+0305'' 

\refer [AUB93.1]  Aubourg, E., Bareyre, P., Br{\'e}hin, S., Gros, M., Lachl{\`e}ze-Rey, M. et al.:  1993, {\sl Nature\/} {\bf 365},  623, ``Evidence for gravitational microlensing by dark objects in the Galactic halo''

\refer [AUB95.1] EROS collaboration: Aubourg, E., Bareyre, P., Brehin, S., Gros, M., Lachieze-Rey, M., Laurent, B., Lesquoy, E., Magneville, C., Milsztajn, A., Moscoso, L., Queinnec, F., Rich, J., Spiro, M., Vigroux, L., Zylberajch, S., Ansari, R., Cavalier, F. Moniez, M., Beaulieu, J.P., Ferlet, R., Grison, Ph., Vidal-Madjar,  A., Maurice, E., Prevot, L., Gry, C., Guibert, J., Moreau, O., Tajahmady, F.:  1995, {\sl Astron. Astrophys.\/} {\bf  301},  1, ``Search for very low-mass objects in the Galactic Halo''

\refer [AVN81.1]  Avni, Y.:  1981, {\sl  Astrophys. J.\/} {\bf  248},  L95, ``On gravitational lenses and the cosmological evolution of quasars'' 

\refer [AVN88.1]  Avni, Y., Shulami, I.:  1988, {\sl  Astrophys. J.\/} {\bf  332},  113, ``"Flux conservation" by a Schwarzschild gravitational lens'' 

\refer [BAB91.1]  Babul, A., Lee, M.H.:  1991, {\sl  Monthly Notices Roy. Astron. Soc.\/} {\bf  250},  407, ``Gravitational lensing by smooth inhomogeneities in the Universe'' 

\refer [BAB87.1]  Babul, A., Paczy{\'n}ski, B., Spergel, D.:  1987, {\sl  Astrophys. J.\/} {\bf  316},  L49, ``Gamma-ray bursts from superconducting cosmic strings at large redshifts'' 

\refer [BAC83.1]  Bacon, R., Nieto, J.-L.:  1983, {\sl  Nature\/} {\bf  301},  400, ``Optical variability of QSOs and gravitational lenses in galactic haloes'' 

\refer [BAC83.2]  Bacon, R., Nieto, J.-L.:  1983, {\sl  IAU Symposium\/} {\bf  104},  381, ``Statistical analysis of optically variable QSOs and bright galaxies - a hint for gravitational lenses'' 

\refer [BAD97.1]  Bade, N., Siebert, J., Lopez, S., Voges, W., Reimers, D.:  1997, {\sl Astron. Astrophys.\/} {\bf  317},  L13, ``RX J0911.4+0551: A new multiple QSO selected from the ROSAT All-Sky Survey''

\refer [BAG95.1]  Baganoff, K. Malkan, M.A.:  1995, {\sl Astrophys. J.\/} {\bf  444},  L13, ``Gravitational microlensing is not required to explain quasar variability'' 

\refer [BAG95.1]  Bagchi, J., Kapahi, V.K.:  1995, {\sl Journ. of Astrophys. Astron., (Suppl. to Vol.16)\/} {\bf  16},  131, ``A new population of gravitationally lensed radio arcs in distant Abell clusters"

\refer [BAH86.1]  Bahcall, J.N., Bahcall, N.A., Schneider, D.P.:  1986, {\sl  Nature\/} {\bf  323},  515, ``Multiple quasars for multiple images'' 

\refer [BAH94.1]  Bahcall, J.N., Flynn, C., Gould, A., Kirhakos, S.:  1994, {\sl  Astrophys. J.\/} {\bf  435},  L51, ``M dwarfs, microlensing, and the mass budget of the galaxy''

\refer [BAH92.1]  Bahcall, J.N., Hartig, G.F., Jannuzi, B.T., Maoz, D., Schneider, D.P.:  1992, {\sl  Astrophys. J.\/} {\bf  400},  L51, ``Faint object spectrograph observations of the large-redshift gravitational lens candidate 1208+1011'' 

\refer [BAH92.2]  Bahcall, J.N., Maoz, D., Doxsey, R., Schneider, D.P., Bahcall, N.A., Lahav, O., Yanny, B.:  1992, {\sl  Astrophys. J.\/} {\bf  387},  56, ``The snapshot survey: a search for gravitationally lensed quasars with the Hubble Space Telescope'' 

\refer [BAH92.3]  Bahcall, J.N., Maoz, D., Schneider, D.P., Yanny, B., Doxsey, R.:  1992, {\sl  Astrophys. J.\/} {\bf  392},  L1, ``HST imaging of the large-redshift gravitational lens candidate 1208+1011'' 

\refer [BAI93.1]  Baillon, P., Bouquet, A., Giraud-H{\'e}raud, Y., Kaplan, J.:  1993, {\sl Astron. Astrophys.\/} {\bf 277},  1, ``Detection of brown dwarfs by the micro-lensing of unresolved stars'' 

\refer [BAL80.1]  Balonek, T.J., Dent, W.A.:  1980, {\sl  Astrophys. J.\/} {\bf  240},  L3, ``A second radio-optical outburst in the BL Lacertae-type quasi-stellar object 0235+164'' 

\refer [BAN91.1]  Bania, T.M., Marscher, A.P.:  1991, {\sl  Astron. J.\/} {\bf  101},  2147, ``Observations of local interstellar CO toward four compact extragalactic radio sources'' 

\refer [BAO94.1]  Bao, G., Hadrava, P., Ostgaard, E.:  1994, {\sl  Astrophys. J.\/} {\bf  435},  55, ``Emission-line profiles from a relatavistic accretion disk and the role of its multiple images''

\refer [BAR96.3]  Bar-Kana, R.:  1996,  {\sl Astrophys. J.\/} {\bf  468},  17, ``Effect of large-scale structure on multiply imaged sources''

\refer [BAR91.1]  Bareyre, P., Maurice, E., Pr{\'e}vot, L., Spiro, M.:  1991, {\sl  La Recherche\/} {\bf  22},  247, ``Comment voir la masse cach{\'e}e des galaxies?'' 

\refer [BAR65.1]  Barnothy, J.M.:  1965, {\sl  Astron. J.\/} {\bf  70},  666, ``Quasars and the gravitational image intensifier'' 

\refer [BAR66.1]  Barnothy, J.M.:  1966, {\sl  The Observatory\/} {\bf  86},  115, ``An observational test of the hypothesis that quasars are produced by gravitational  lenses'' 

\refer [BAR68.1]  Barnothy, J.M., Barnothy, M.F.:  1968, {\sl  Science\/} {\bf  162},  348, ``Galaxies as gravitational lenses'' 

\refer [BAR71.1]  Barnothy, J.M., Barnothy, M.F.:  1971, {\sl  Bull. AAS\/} {\bf  3},  472, ``Rapid differential proper motion in the radio fine structure of 3C279'' 

\refer [BAR72.1]  Barnothy, J.M., Barnothy, M.F.:  1972, {\sl  Astrophys. J.\/} {\bf  174},  477, ``Expected density of gravitational-lens quasars'' 

\refer [BAR86.1]  Barnothy, J.M., Barnothy, M.F.:  1986, {\sl  Astron. J.\/} {\bf  91},  755, ``Morphological aberration on gravitational-lens images'' 

\refer [BAR87.1]  Barrow, J.D., Subramanian, K.:  1987, {\sl  Nature\/} {\bf  327},  375, ``Lensing of supernova neutrinos'' 

\refer [BAR93.1]  Bartelmann, M.:  1993, {\sl  Astron. Astrophys.\/} {\bf  276},  9, ``Consequences of cluster evolution for the statistics of giant luminous arcs'' 

\refer [BAR95.7]  Bartelmann, M.:  1995, {\sl Astron. Astrophys.\/} {\bf  299},  11, ``Arc statistics with realistic cluster potentials. III. A systematic effect on cluster mass estimates''

\refer [BAR95.8]  Bartelmann, M.:  1995, {\sl Astron. Astrophys.\/} {\bf  298},  661, ``Cosmological parameters from angular correlations between QSOs and galaxies''

\refer [BAR95.10]  Bartelmann, M.:  1995, {\sl Astron. Astrophys.\/} {\bf  303},  643, ``Cluster mass estimates from weak lensing''

\refer [BAR96.5]  Bartelmann, M.:  1996, {\sl  Astron. Astrophys.\/} {\bf  313},  697, ``Arcs from a universal dark-matter halo profile''

\refer [BAR96.1]  Bartelmann, M., Loeb, A.:  1996, {\sl Astrophys. J.\/} {\bf  457},  529, ``Gravitational lensing of quasi-stellar objects by their damped lyman-alpha absorbers''

\refer [BAR95.3]  Bartelmann, M., Narayan, R.:  1995, {\sl Astrophys. J.\/} {\bf  451},  60, ``The lens parallax method: determining the redshifts of the faint blue galaxies through gravitational lensing''

\refer [BAR95.9]  Bartelmann, M., Narayan, R.:  1995, {\sl  AIP Conf. Proceedings 336, ``Dark Matter'', College Park, MD, Oct.94 (eds. Holt, S.S., Bennett, C.L.W)\/},  p.307, ``Gravitational lensing and the mass distribution of clusters''

\refer [BAR96.2]  Bartelmann, M., Narayan, R., Seitz, S., Schneider, P.:  1996, {\sl Astrophys. J.\/} {\bf 464},  L115, ``Maximum likelihood cluster reconstruction''

\refer [BAR90.2]  Bartelmann, M., Schneider, P.:  1990, {\sl  Astron. Astrophys.\/} {\bf  239},  113, ``Influence of microlensing on quasar statistics'' 

\refer [BAR91.2]  Bartelmann, M., Schneider, P.:  1991, {\sl  Astron. Astrophys.\/} {\bf  248},  349, ``Gravitational lensing by large-scale structures'' 

\refer [BAR92.2]  Bartelmann, M., Schneider, P.:  1992, {\sl  Astron. Astrophys.\/} {\bf  259},  413, ``A large-scale structure model for gravitational lensing'' 

\refer [BAR92.3]  Bartelmann, M., Schneider, P.:  1992, {\sl  Astron. Astrophys.\/} {\bf  268},  1, ``Large-scale correlations between QSOs and galaxies. An effect caused by gravitational lensing?'' 

\refer [BAR93.2]  Bartelmann, M., Schneider, P.:  1993, {\sl  Astron. Astrophys.\/} {\bf  271},  421, ``Large-scale QSO-galaxy correlations revisited'' 

\refer [BAR94.3]  Bartelmann, M., Schneider, P.:  1994, {\sl Astron. Astrophys.\/} {\bf  284},  1, ``Large-scale correlations between QSOs and IRAS galaxies''
 (Erratum: 1995, {\sl  Astron. Astrophys.\/} {\bf  295}, 565)

\refer [BAR94.2]  Bartelmann, M., Schneider, P., Hasinger, G.:  1994, {\sl Astron. Astrophys.\/} {\bf  290}, 399, ``Diffuse X-ray emission around high-redshift, radio-loud QSOs''

\refer [BAR96.7]  Bartelmann, M., Steinmetz, M.:  1996, {\sl Monthly Notices Ro. Astron. Soc.96\/} {\bf  283}, 431, ``A omparison of X-ray and strong lensing properties of simulated X-ray Clusters''

\refer [BAR95.1]  Bartelmann, M., Steinmetz, M., Weiss, A.:  1995, {\sl Astron. Astrophys.\/} {\bf  297}, 1, ``Arcs statistics with realistic cluster potentials. II.Influence of cluster asymmetry and substructure''

\refer [BAR94.1]  Bartelmann, M., Weiss, A.:  1994, {\sl Astron. Astrophys.\/} {\bf  287},  1, ``Arc statistics with realistic cluster potentials. I. Method and first results''

\refer [BAR94.11] Barvainis, R.:  1994, {\sl Proc. of Oxford Torus Workshop, ed. M.J.Ward\/},  p.81, ``CO and CI in the Cloverleaf, a quasar z=2.5''

\refer [BAR92.4]  Barvainis, R., Antonucci, R., Coleman, P.:  1992, {\sl  Astrophys. J.\/} {\bf  399},  L19, ``Submillimeter observations of radio-quiet quasars and a luminous Seyfert 1 galaxy including the first detections'' 

\refer [BAR95.6]  Barvainis, R., Antonucci, R., Hurt, T., Coleman, P., Reuter, H.-P.:  1995, {\sl Astrophys. J.\/} {\bf  451},  L9, ``The broadband spectral energy distributions of the cloverleaf quasar and IRAS F10214+4724''

\refer [BAR94.4]  Barvainis, R., Tacconi, L., Antonucci, R., Alloin, D., Coleman, P.:  1994, {\sl Nature\/} {\bf 371},  586, ``Extremely strong carbon monoxide emission from the cloverleaf quasar at a redshift of 2.5''

\refer [BAU94.1]  Bautz, M.W., Crew, G.B., Gendreau, K.C., Mushotsky, R., Arnaud, K.A. et al.:  1994, {\sl Proc. of New Horizons of X-ray astronomy-First results from ASCA\/},  p.285, ``ASCA observations of distant clusters of galaxies''

\refer [BAU94.2]  Bautz, M.W., Mushotsky, R., Fabian, A.C., Yamashita, K., Gendreau, K.C. et al.:  1994, {\sl Publ. Astron. Soc. Japan\/} {\bf  46},  L131, ``ASCA detection of iron line emission from the distant galaxy cluster Abell 370''

\refer [BAZ87.1]  Bazin, M.J., De Freitas, L.:  1987, {\sl  Astrophys. Space Science\/} {\bf  138},  381, ``True Gravitational lens effect for cylindrical deflectors'' 

\refer [BEA92.1]  Beauchemin, M., Borra, E.F.:  1992, {\sl  Astrophys. J.\/} {\bf  103},  405, ``An automated search for widely spaced gravitational lenses performed on 25 grens plates'' 

\refer [BEA95.1]  Beaulieu, J.P., Ferlet, R., Grison, Ph., Vidal-Madjar, A., Kneib, J.P. et al.: 1995,  {\sl Astron. Astrophys.\/} {\bf  299},  168, ``Spectroscopic studies of the two EROS candidate microlensed stars''

\refer [BEC94.1]  Bechtold, J., Crotts, A.P.S., Duncan, R.C., Fang, Y.:  1994,  {\sl Astrophys. J.\/} {\bf  437},  L83, ``Spectroscopy of the double quasars Q1343+266A,B:  A new determination of the size of Ly-$\alpha$ forest absorbers''

\refer [BEC95.1]  Bechtold, J., Yee, H.K.C.:  1995, {\sl Astron. J.\/} {\bf  110\/}, 1984,  ``High spatial resolution spectroscopy of the Ly $\alpha$ absorption towards the gravitational lens system B 1422+2309''

\refer [BEG87.1]  Begelman, M.C., Blandford, R.D.:  1987, {\sl  Nature\/} {\bf  330},  46, ``Luminous arcs from galactic bow shocks'' 

\refer [BEK94.1]  Bekenstein, J.D., Sanders, R.H.:  1994, {\sl Astrophys.J.\/} {\bf 429},  480, ``Gravitational lenses and unconventional gravity theories''

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\newpage

\noindent {\Large \bf Conference Proceedings and Books}\\

%\vs

\par

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``Gravitational lenses in the Universe''

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\newpage

\noindent {\Large \bf Preprints, submitted papers and recently published articles}\\

%\vs

\par


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\refer [ALC96.3]  Alcock, C., Allsman, R.A., Alves, D., Axelrod, T.S., Becker, A. et al.:  1996, {\sl Astrophys. J., Nov.96\/} {\bf  471},  774, ``The MACHO Project: Limits on Planetary Mass Dark Matter in the Galactic Halo from Gravitational Microlensing''

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\refer [ANS96.3] *Ansari, R., Auri\'ere, M., Baillon, P., Bouquet, A., Coupinot, G. et al.:  1996, {\sl submitted, Jul.96\/},  `` AGAPE: a search for dark matter towards M31 by microlensing effects on unresolved stars''

\refer [ANS96.1]  Ansari, R., Cavalier, F., Moniez, M., Aubourg, E., Bareyre, P. et al.:  1996, {\sl Astron. Astrophys., Oct.96\/} {\bf  314},  94, ``Observational limits on the contribution of substellar and stellar objects to the galactic halo''

\refer [ASA96.2] *Asada, H.:  1996,  {\sl Astrophys. J., submitted, Nov.96\/}, ``Critical Lines in Gravitational Lenses and the Determination of Cosmological Parameters''

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\refer [BAO96.1]  Bao, G., Wiita, P.J.:  1996,  {\sl Astrophys. J., submitted, Jul.96\/}, ``Is the counterjet in NGC 1275 gravitationally lensed?''

\refer [BAR96.3]  Bar-Kana, R.:  1996,  {\sl Astrophys. J., Sep.96\/} {\bf  468},  17, ``Effect of large-scale structure on multiply imaged sources''

\refer [BAR96.4] *Bar-Kana, R.:  1996,  {\sl Phys. Rev. D., in press, 15 Dec.\/}, ``Limits on a Stochastic Background of Gravitational Waves from Gravitational Lensing''

\refer [BAR97.1] *Bar-Kana, R.:  1997,  {\sl Astrophys. J., submitted, Jan.97\/}, ``Analysis of time delays in the gravitational lens PG1115+080'' 

\refer [BAR96.5]  Bartelmann, M.:  1996, {\sl  Astron. Astrophys., Sep.96\/} {\bf  313},  697, ``Arcs from a universal dark-matter halo profile''

\refer [BAR96.1]  Bartelmann, M., Loeb, A.:  1996, {\sl Astrophys. J., Feb.96\/}, {\bf  457},  529, ``Gravitational lensing of quasi-stellar objects by their damped lyman-$\alpha$ absorbers''

\refer [BAR96.2]  Bartelmann, M., Narayan, R., Seitz, S., Schneider, P.:  1996, {\sl Astrophys. J., Jun.96\/} {\bf 464},  L115, ``Maximum likelihood cluster reconstruction''

\refer [BAR96.7]  Bartelmann, M., Steinmetz, M.:  1996, {\sl Monthly Notices Ro. Astron. Soc., Nov.96\/} {\bf  283}, 431, ``A omparison of X-ray and strong lensing properties of simulated X-ray Clusters''

\refer [BAR96.6] *Bartsch, A., Schneider, P., Bartelmann, M.:  1996,  {\sl Astron. Astrophys., submitted, Jan.96\/}, ``Reanalysis of the association of high-redshift 1-Jansky quasars with IRAS galaxies''

\refer [BAR95.4]  Barvainis, R.:  1995, {\sl Astron. J., in press\/}, ``Non-confirmation of extreme CO(1-0) line emission from IRAS F10214+4724''

\refer [BAR95.5]  Barvainis, R.:  1995, {\sl IAU Symp. 170, in press\/}, ``CO (and other) lines from the Cloverleaf quasar''

\refer [BAR97.1] *Barvainis, R., Maloney, Ph., Antonucci, R., Alloin, D.:  1997, {\sl Astrophys. J., in press, Mar.97\/}, ``Multiple CO Transitions, CI, and HCN from the Cloverleaf Quasar''

\refer [BEN96.1] *Benitez, N., Martinez-Gonzales, E.:  1996, {\sl Astrophys. J., in press, Sep.96\/}, ``Large Scale QSO-galaxy correlations for radio loud and optically selected QSO samples''

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\refer [BER96.1]  *Berezinsky, V., Bottino, A., Mignola, G.:  1996, {\sl submitted, Oct.96\/},  ``On neutralino stars as microlensing objects''

\refer [BER96.2]  *Bernardeau, F.:  1996, {\sl Astron. Astrophys., submitted, Oct.96\/}, ``Weak Lensing Detection in CMB Maps''

\refer [BER97.1]  *Bertolami, O.:  1997, {\sl Gen. Relativity and Gravitation, in press, Feb.97\/},  ``Weak Lensing, Shear and the Cosmic Virial Theorem in a Model with a Scale-Dependent Gravitational Coupling''

\refer [BEZ96.1]  *Bezecourt, J., Soucail, G.:  1996, {\sl Astron. Astrophys., in press, Jun.96\/}, ``Redshift survey of gravitational arclets in Abell 2390''

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\refer [BLO96.1]  Bloomfield Torres, L.F., Waga, I.:  1996,  {\sl Monthly Notices Roy. Astron. Soc., Apr.96\/} {\bf  279}, 712, ``Decaying $\Lambda$ cosmologies and statistical properties of gravitational lenses''

\refer [BOG96.1]  Bogdanov, M.B., Cherepashchuk, A.M.:  1996, {\sl Astronomy Reports, Oct.96\/} {\bf  40},  713, ``Reconstruction of the brightness distribution over a stellar disk from observations of gravitational microlensing''

\refer [BON96.1]  Bondi, M., Garrett, M., Gurvits, L.:  1996,  {\sl Proc. IAU Symp. 175, in press, Jan.96\/},  ``PKS 1117 gravitational lens or micro-lobes''

\refer [BOR96.1] *Borra, E.F., Ferrari, M., Girard, L., Moretto, G., Tremblay, G., Lemaitre, G.:  1996,  {\sl SPIE conference proceedings 'Optical Telescopes of Today and Tomorrow', May 29 - June1, Landskrona/Hven, Sweden\/},  ``Liquid Mirror Telescopes: A progress report''

\refer [BOU96.1]  Boutreux, Th., Gould, A.: 1996, {\sl Astrophys. J., May,96\/}{\bf  462},  705, ``Monte Carlo simulations of MACHO parallaxes from a satellite''

\refer [BOW96.1] *Bower, R.G., Smail, I.: 1996, {\sl Monthly Notices Roy. Astron. Soc., Dec.96\/},  ``A Weak Lensing Survey in the Fields of z~1 Luminous Radio Sources''

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\refer [BRA96.1]  Brainerd, T., Blandford, R., Smail, I.:  1996, {\sl Astrophys. J., Aug.96\/} {\bf  466}, 623,  ``Weak gravitational lensing by galaxies''

\refer [BRO96.1]  Bromley, B.C.:  1996, {\sl Astrophys. J., Aug.96\/} {\bf  467},  537, ``Finite-size gravitational microlenses''

\refer [BRO95.5] *Broadhurst, T.:  1995, {\sl  Astrophys. J. Letters, submitted, Nov.95\/}, ``Gravitational `Convergence' and cluster masses''

\refer [BUC96.2] *Buchalter, A., Kamionkowski, M.: 1996, {\sl  Astrophys. J., submitted, Apr.96\/}, ``Rates for Parallax-Shifted Microlensing Events from Ground-Based Observations of the Galactic Bulge''

\refer [BUC96.1]  Buchalter, A., Kamionkowski, M., Rich, R.M.: 1996, {\sl  Astron. J., Oct..96\/} {\bf  469},  676, ``Rates for color shifted microlensing events''

\refer [BUR96.1]  Burbidge, E.M., Beaver, E.A., Cohen, R.D., Junkkarinen,, V.T., Lyons, R.W.:  1996, {\sl Astron. J., submitted, Aug.96\/},  ``AO 0235+164 and surrounding field: surprising HST results''

\refer [BUR96.1] *Burbige, G., Hoyle, F., Schneider, P.:  1996, {\sl Astron. Astrophys. Let., submitted, Jan.96\/}, ``Very close pairs of quasi-stellar objects''

\refer [CAP96.1] *Capozziello, S., de Ritis, R., Mank'o, V., Marino, A.A., Marmo, G.:  1996, {\sl Phys. Let. A, submitted, Oct.96\/},  ``Luminosity variation in (de)focusing microlensing''

\refer [CAP96.1] *Capozziello, S., de Ritis, R., Mank'o, V., Marino, A.A., Marmo, G.:  1996, {\sl Physica Scripta, submitted, Oct.96\/},  ``Defocusing gravitational microlensing''

\refer [CAS96.1]  Casoli, F., Encrenaz, P., Fort, B., Boiss{\'e}, P., Mellier, Y.:  1996, {\sl Astron. Astrophys., Feb.96\/}, {\bf  306},  L41, ``CO lines from giant arcs in clusters''

\refer [CHA96.1]  Chabrier, G., Segretain, L., M{\'e}ra, D.:  1996,  {\sl Astrophys. J., Sep.96\/} {\bf  468},  L21, ``Contribution of brown dwarfs and white dwarfs to recent microlensing observations and to the halo mass budget''

\refer [CHA95.2]  Charlton, J., Linder, S., Churchill, C.:  1995, {\sl  Astrophys. J., in press\/},  ``Probing Lyman $\alpha$ absorbers with double lines of sight''

\refer [CHA97.1]  Chavushyan, V.H., Vlasyuk, V.V., Stepanian, J.A., Erastova, L.K.:  1997,  {\sl Astron. Astrophys.\/} {\bf  318},  L67, ``SBS 1520+530: a new gravitationally lensed system at z=1.855''

\refer [CHI96.1]  Chiba, M., Yoshii, Y.:  1996,  {\sl Astrophys. J., submitted, Jul.96\/}, ``Gravitational lensing of quasars by damped lyman-$\alpha$ absorption systems''

\refer [CHI96.2]  Chiba, M., Yoshii, Y.:  1996,  {\sl Astrophys. J., submitted, Jul.96\/}, ``Does the lensing statistics rule out a cosmological constant?''

\refer [CLA96.1]  Claeskens, J.-F, Surdej, J., Remy, M.:  1996,  {\sl  Astron. Astrophys., Jan.96\/}, {\bf  305},  L9, ``J03.13A and B: a new multiply imaged QSO candidate''

\refer [COC96.1]  Cocks, F.H., Cocks, E.E.:  1996,  {\sl Icarus, submitted, Sep.96\/}, ``Stellar ocultation and a dark-lens diffracting telescope: a novel approach to direct extrasolar planetary detection''

\refer [COL96.1]  Colley, W.N., Tyson, J.A., Turner, E.L.:  1996, {\sl Astrophys. J., Apr.96\/}, {\bf  461},  L83, ``Unlensing multiple arcs in 0024+1654: reconstruction of the source image''

\refer [CRA96.1]  Crampton, D., Le F{\`e}vre, O., Hammer, F., Lilly, S.J.:  1996,  {\sl Astron. Astrophys., Mar.96\/}, {\bf  307},  L53, ``The gravitational lens CFRS14.1311 = HST 14176+5226''

\refer [CRI96.1]  Cristiani, S., Trentini, S., La Franca, F., Aretxaga, I., Andreani, P., Vio, R., Gemmo, A.:  1996, {\sl Astron. Astrophys., Feb.96\/}, {\bf 306},  395, ``The optical variability of QSOs''

\refer [CRO96.3] *Crone, M., Governato, F., Stadel, J., Quinn, T.:  1996, {\sl  Astrophys. J. Let., submitted, Oct.96\/},  ``Prospects for Cosmology with Cluster Mass Profiles''

\refer [CRO96.1] *Crotts, A.P.S.:  1996, {\sl International Conference on "Dark and Visible Matter in Galaxies", Sesto Pusteria, Italy, Jul.96\/},  ``VATT/Columbia Microlensing Survey of M31 and the Galaxy''

\refer [CRO96.2]  Crotts, A.P.S., Tomaney, A.B.:  1996, {\sl  Astrophys. J., Dec.96\/} {\bf  473},  L87, ``Results from a Survey of Gravitational Microlensing towards M31''

\refer [DE~96.1]  de Gouveia Dal Pino, E.M., Horvath, J.E., de Freitas Pacheco, J.A.:  1996, {\sl Astrophys. J. Letters, Jan.96\/}, {\bf 456},  L97, ``The role of thermal instabilities on the theoretical mass function of MACHOs''

\refer [DE~97.1] *de Laix, A.A., Krauss, L.M., Vachaspati, T.:  1997, {\ submitted, Feb.97\/},  ``Gravitational Lensing Signature of Long Cosmic Strings''

\refer [DE~96.3] *de Laix, A.A., Vachaspati, T.:  1996, {\ submitted, May,96\/},  ``Gravitational Lensing by Cosmic String Loops''

\refer [DE~96.2]  De Paolis, F., Ingrosso, G., Jetzer, P.:  1996, {\sl Astrophys. J., Aug.96\/} {\bf  470},  493, ``Microlensing rates from self-consistent galactic models''

\refer [DEL96.2]  Dell'Antonio, I.P., Tyson, J.A.:  1996, {\sl Astrophys. J., Dec.96\/} {\bf  473},  L17,  ``Galaxy Dark Matter: Galaxy-galaxy lensing in the Hubble Deep Field'' 

\refer [DEL96.1]  Della Valle, M., Livio, M.:  1996, {\sl Astrophys. J., Jan.96\/}, {\bf  457}, L77, ``Are microlensing events contaminated by dwarf nova eruptions?''

\refer [DI~96.1]  Di Stefano, R., Mao, S.:  1996, {\sl Astrophys. J., Jan.96\/}, {\bf  457},  93, ``Do microlensing events repeat?''

\refer [DI~96.2]  Di Stefano, R., Perna, R.:  1996, {\sl Astrophys. J., Dec.96\/},  ``Microlensing by binaries: identifying the gentle perturbations''

\refer [DI~97.1] *Di Stefano, R., Perna, R.:  1997, {\sl Astrophys. J., Feb.97\/},  ``Identifying Microlensing by Binaries''

\refer [DOL95.1]  Dolan, J.F.:  1995, {\sl Astron. J., submitted\/}, ``High speed photometer observations of Q2345+007 in the ultraviolet: the gravitational lens interpretation''

\refer [DOM97.1] *Dominik, M.:  1997, {\sl Astron. Astrophys., submitted, Jan.97\/},  ``Estimating physical quantities for an observed galactic microlensing''

\refer [DOM97.2] *Dominik, M.:  1997, {\sl submitted, Feb.97\/},  ``Galactic microlensing with rotating binaries''

\refer [DOM97.3] *Dominik, M.:  1997, {\sl submitted, Feb.97\/},  ``Ambiguities in fits of binary lens galactic microlensing events

\refer [DOM96.1]  Dominik, M., Hirshfeld, A.C.:  1996, {\sl Astron. Astrophys., Sep.96\/} {\bf  313},  841,  ``Evidence for a binary lens in the MACHO LMC No.1 microlensing event''

\refer [DRE96.1] *Dressler, A., Smail, I.:  1996, {\sl  Proc. of the 37th Herstmonceux conference ``HST and the  High Redshift Universe''\/}, ``HST Observations of Distant Clusters: Implications for Galaxy Evolution''

\refer [DRI96.1]  Driver, S.P., Couch, W.J., Phillipps, S., Windhorst, R.A.:  1996, {\sl Astrophys. J., in press, Aug.96\/}, ``The inferred redshift distribution of the faint blue excess''

\refer [EBB96.1]  Ebbels,T.M.D., Le Borgne, J.-F., Pell{\'o}, R., Ellis, R.S., Kneib, J.-P. et al.:  1996, {\sl Monthly Notices Roy. Astron. Soc., Aug.96\/} {\bf  281},   L75, ``Identification of a Gravitationally Lensed z=2.515 Star-Forming Galaxy''

\refer [EBB97.1] *Ebbels,T.M.D., Ellis, R.S., Kneib, J.-P., Le Borgne, J.-F., Pell{\'o}  et al.:  1997, {\sl Monthly Notices Roy. Astron. Soc., submitted, Mar.97\/}, ``Spectroscopic Confirmation of Redshifts Predicted by Gravitational
  Lensing''

\refer [EIS95.1]  Eisenhard,P.R., Armus, L., Hogg, D.W., Soifer, B., Neugebauer, G., Werner, W.:  1995, {\sl Astrophys. J., submitted, Jul.95\/}, ``HST observations of the luminous IRAS source FSC10214+4724: a gravitationally lensed infrared quasar''

\refer [ELL96.1]  Ellithorpe, Kochanek, C.S., Hewitt, J.N.:  1996, {\sl Astrophys. J., Jun.96\/} {\bf  464},  556, ``Visibility lensclean and the reliability of deconvolved radio images''

\refer [EVA95.1]  Evans, N.W.:  1995,  {\sl Astrophys. J., submitted\/}, ``The optical depth to microlensing towards the galactic bulge''

\refer [EVA96.1]  Evans, N.W.:  1996,  {\sl Monthly Notices Roy. Astron. Soc., Jan.96\/}, {\bf  278},  L5, ``The nature of the galactic dark matter''

\refer [FAL96.1]  Falco, E.E., Leh{\'a}r, J., Perley, R.A., Wambsganss, J.,Gorenstein, M.V.:  1996, {\sl Astron. J., Sep.96\/} {\bf  112},  897, ``VLA observations of the gravitational lens system Q2237+0305''

\refer [FAL97.1]  Falco, E.E., Leh{\'a}r, J., Shapiro, I.: 1997, {\sl Astron. J., Feb.97\/} {\bf  113},  540, ``HST observations and models of the gravitational lens system MG 0414+0534''

\refer [FAL97.1] *Falco, E.E., Shapiro, I.I., Moustakas, L.A., Davis, A.:  1997, {\sl Astrophys. J., in press, Feb.97\/}, ``An estimate of $H_0$ from Keck spectroscopy of the gravitational lens system 0957+561''

\refer [FAR96.1] *Faraoni, V.:  1996, {\sl Proc. of the Pacific Conference on Gravitation and Cosmology, Seoul, Korea, 1996\/}, ``The creation of multiple images by a gravitational wave''

\refer [FAS96.1]  Fassnacht, D., Womble, D.S., Neugebauer, G., Browne, I.W.A., Readhead, A.C.S. et al.:  1996, {\sl Astrophys. J., Apr.96\/}, {\bf  460}, L103, ``1608+656: A gravitationally lensed poststarburst radio galaxy''
 
\refer [FER95.1]  Ferlet, R.:  1995, {\sl Relativ. Astrophys., submitted\/}, ``Machos and dark matter''

\refer [FIS97.1]  Fischer, P., Bernstein, G., Rhee, G., Tyson, J.A.: 1997, {\sl Astron. J., Feb.97\/} {\bf  113},  521, ``The mass distribution of the cluster 0957+561 from gravitational lensing''

\refer [FIS97.1] *Fischer, P., Tyson, J.A.: 1997, {\sl Astron. J., in press, Mar.97\/}, ``The mass distribution of the most luminous X-ray cluster RXJI347.5-1145 from gravitational lensing''

\refer [FLO96.1]  Flores, R.A., Primack, J.R.:  1996, {\sl Astrophys. J., Jan.96\/}, {\bf  457},  L5, ``Cluster cores, gravitational lensing and cosmology''

\refer [FOR96.1]  Fort, B., Mellier, Y., Dantel-Fort, M.,Bonnet, H., Kneib, J.-P.: 1996, {\sl Astron. Astrophys., Jun.96\/} {\bf 310}, 705, ``Observations of weak lensing in the fields of luminous radiosources'' 

\refer [FOR96.2]  *Fort, B., Mellier, Y., Dantel-Fort, M.:  1996,  {\sl Astron. Astrophys., submitted, Jun.96\/}, ``Distribution of galaxies at large redshift and cosmological parameters from the magnification bias in Cl0024+1654''

\refer [FRI97.1]   Fried, J.W.: 1997, {\sl Astron. Astrophys., Mar.97\/} {\bf  319},  365, ``Faint galaxies around quasars at z = 1 and gravitational lensing of distant objects'' 

\refer [FRI96.1] *Frieman, J.A.:  1996, {\sl Comments on Astrophysics, in press, Aug..96\/}, ``Weak Lensing and the Measurement of q0 from Type Ia Supernovae''

\refer [FRY96.1]  Frye, B., Welch, Wm.J., Broadhurst, T.:  1996, {\sl Astrophys. J., submitted, Aug.96\/}, ``Resolving redshifted molecular absorptin towards the lens PKS 1830-211'' 

\refer [FUK96.1]  Fukugita, M., Ichikawa, T., Gunn, J.E., Doi, M. et al.:  1996,  {\sl Astron. J., in press, Jan.96\/}, ``The Sloan Digital Sky Survey photometric system''                   

\refer [FUK97.1] *Fukuyama, T., Okamura, T.:  1997,  {\sl Astrophys. J., submitted, Jan.97\/}, ``On the general theorems about the gravitational lensing''

\refer [GAR96.2]  Garrett, M.A., Porcas, R.W., Nair, S., Patnaik, A.R.:  1996, {\sl Monthly Notices Roy. Astron. Soc., Mar.96\/}, {\bf  279}, L7, ``Wide-field EVN observations of the gravitational lens system 2016+112''

\refer [GAT95.2] *Gates, E.I., Gyuk, G., Turner, M.S.:  1995, {\sl Phys. Rev. D, submitted\/}, `` Gravitational microlensing and the galactic halo''

\refer [GAU97.1]  Gaudi, B.S., Gould, A.:  1997, {\sl Astrophys. J., Mar.97\/} {\bf  477}, 152,  ``Satellite parallaxes of lensing events towards the Galactic Bulge''

\refer [GAU96.2] *Gaudi, B.S., Gould, A.:  1996, {\sl Astrophys. J., submitted, Jun.96\/}, ``Detection rates for close binaries via microlensing''

\refer [GAU96.3] *Gaudi, B.S., Gould, A.:  1996, {\sl Astrophys.J., submitted, Oct.96\/}, ``Planet Parameters in Microlensing Events''

\refer [GEI97.1] *Geiger, B.:  1997, {\sl Proc. of the ESO Workshop on Galaxy Scaling Relations: Origins, Evolution and Applications, Nov.96\/},  ``Constraining the Mass Distribution of Cluster Galaxies by Weak Lensing''

\refer [GEI96.1]  Geiger, B., Schneider, P.:  1996,  {\sl Monthly Notices Roy. Astron. Soc., Oct.96\/} {\bf  282},  530, ``The light-curve reconstruction method for measuring the time delay of gravitational lens systems''

\refer [GER95.1] *Gerhard, O., Silk, J.:  1995, {\sl submitted, Sep.95\/}, ``Baryonic dark halos: MACHOs and cold gas''

\refer [GIO96.1] *Gioia, I.:  1996, {\sl Proc. ``Mapping, Measuring and Modelling the Universe'', Valencia 1995, eds. P. Coles and V. Martinez, in press, Jan.96\/}, ``X-ray selected clusters of galaxies''

\refer [GIO96.2]  Gioia, I.M., Shaya, E.J., Le F{\`e}vre, O., Falco, E.E., Luppino, G.A., Hammer, F.:  1996,  {\sl Astrophys. J., submitted, Dec.96\/},  ``The lensing cluster MS0440+02 seen by HST, ROSAT and ASCA. I. Cluster properties'' 
\refer [GON96.1] *Gondolo, P., Ansari, R., Auriere, M., Baillon, P., Bouquet, G. et al.:  1996, {\sl Proc. International Conference on "Dark and Visible Matter in Galaxies", Sesto Pusteria, Italy, in press, Jul.96\/}, ``AGAPE: a Microlensing Search for Dark Matter by Monitoring Pixels''

\refer [GOO96.1]  Goodrich, R.W., Miller, J.S., Martel, A., Cohen, M.H., Tran, H.D. et al.:  1996, {\sl Astrophys. J., Jan.96\/}, {\bf 456},  L9, `` FSC 10214+4724: a gravitationally lensed, hidden QSO''

\refer [GOP96.1]  Gopal-Krishna, Subramanian, K.:  1996, {\sl Astron. Astrophys., Nov.96\/} {\bf  315},  343, ``Testing  the lensing hypothesis for compact double radio sources and other milli-lensing candidates''

\refer [GOU96.2]  Gould, A.:  1996, {\sl Astrophys. J., Oct.96\/} {\bf  470},  201, ``Theory of pixel lensing''

\refer [GOU96.3]  Gould, A.:  1996, {\sl Pub. Astron. Soc. Pac., Jun.96\/} {\bf  108},  465, ``Microlensing and the Stellar Mass Function''

\refer [GOU96.4] *Gould, A.:  1996, {\sl Astrophys. J., submitted, Mar.1996\/},  ``Extreme Microlensing''

\refer [GOU96.5] *Gould, A.:  1996, {\sl Four lectures given at College de France, Paris, May,96\/},  ``Les Microlentilles Gravitationnelles''

\refer [GOU96.9] *Gould, A.:  1996, {\sl 12th IAP Colloquium: Variable Stars and the Astrophysical Returns of Microlensing Surveys, Aug.,96\/},  ``The Hollywood Strategy for Microlensing Detection of Planets''

\refer [GOU96.10] *Gould, A.:  1996, {\sl Astrophys. J., submitted, Nov.96\/},  ``Measuring the Rotation Speed of Giant Stars From Gravitational Microlensing''

\refer [GOU96.8] *Gould, A.:  1996, {\sl Sheffield workshop on Identification of Dark Matter, Nov.96\/},  ``Microlensing: Prospects for the Future''

\refer [GOU97.2] *Gould, A.:  1997, {\sl Talk given at 25th Anniversary of Wise Observatory, Mar.97\/},  ``Microlensing: Current Results and Future Prospects''

\refer [GOU96.9] *Gould, A.:  1996, {\sl Sheffield workshop on Identification of Dark Matter, Nov.96\/},  ``Star Counts From HST: Implications for Dark Matter''

\refer [GOU96.6] *Gould, A., Gaudi, S.:  1996, {\sl submitted, Jun.96\/},  ``Femtolens Imaging of a Quasar Central Engine Using a Dwarf Star Telescope''

\refer [GOU97.1]  Gould, A., Gaucherel, C.:  1997, {\sl Astrophys. J., Mar.97\/} {\bf  477 }, 580,   ``Stokes's theorem applied to microlensing of finite sources''

\refer [GOU96.11] *Gould, A., Miralda-Escud{\'e}, J.:  1996, {\sl Astrophys. J., submitted, Dec.96\/},  ``Signatures of Accretion Disks in Quasar Microlensing''

\refer [GOU96.1]  Gould, A., Welch, D.L.: 1996, {\sl Astrophys. J., Jun.96\/} {\bf  464},  212,  ``MACHO proper motions from optical/infrared photometry''

\refer [GRA96.1]  Granato, G.L., Danese, L., Franceschini, A.:  1996, {\sl Astrophys. J., Mar.96\/}  {bf 460}, L11, ``Dust-enshrouded AGN models for hyperluminous, high-redshift infrared galaxies''

\refer [GRI94.1]  Griest, K.:  1994, {\sl  Plenary review talk at Snowmass 94, June,  "Particle and Nuclear Astrophysics and Cosmology in the Next Millennium"\/}, ``The particle- and astro-physics of dark matter''

\refer [GRI95.2] *Griest, K.:  1995, {\sl  Proc. International School of Physics Enrico Fermi Course ``Dark Matter in the Universe'', Varenna, Aug.95\/}, ``The nature of the dark matter''

\refer [GRI95.1] *Griest, K., Alcock, C., Allsman, T.S., Axelrod, D.P., Bennet, K.H. et al. (The MACHO Collaboration):  1995,  {\sl Proc. Pascos/Hopkins Symp., Baltimore, in press}, ``MACHO collaboration search for baryonic dark matter via gravitational microlensing''

\refer [GRI96.1]  Griffiths, R.E., Casertano, S., Im, M., Ratnatunga, K.U.:  1996,  {\sl Monthly Notices Roy. Astron. Soc., Oct.96\/} {\bf  282},  1159, ``Weak Gravitational Lensing around Field Galaxies in Hubble Space Telescope Survey Images''

\refer [GRO96.1]  Grogin, A., Narayan, R.:  1996, {\sl Astrophys. J., Jun.96\/} {\bf  464},  92, ``A new model of the gravitational lens 0957+561 and a limit on the Hubble constant'' (Erratum: 1996, {\sl  Astrophys. J.\/} {\bf  473}, 570)

\refer [GYU96.1] *Gyuk, G.:  1996, {\sl Astrophys. J., submitted, Jul.96\/}, ``Gravitational Microlensing and the Structure of the Inner Milky Way''

\refer [HAA97.1] *Haarsma, D.B., Hewitt, J.N., Leh{\'a}r, J., Burke, B.F.:  1997, {\sl Astrophys. J., to appear, Apr.10,97\/}, ``The 6 cm Light Curves of B0957+561, 1979-1994: New Features and Implications for the Time Delay''

\refer [HAM96.1] *Hamana, T., Hattori, H., Ebeling, H., Henry, J.P., Futamase, T., Shioya, Y.:  1996, {\sl Astrophys. J., in press, Mar..97\/}, ``Lensing effects on the protogalaxy candidate cB58 and their implications for the cosmological constant''

\refer [HAM96.1] *Hammer, F., Teyssandier, P., Shaya, E.J., Gioia, I.M., Luppino, G.A., Le F\`evre, O.:  1996, {\sl Astrophys. J. Let., submitted, Oct.96\/}, ``Detailed lensing properties of the MS2137-2353 core and reconstruction of sources''
 
\refer [HAN96.3]  Han, C.:  1996, {\sl Astrophys. J., Nov.96\/} {\bf  472},  108, ``Pixel lensing experiment towards the M31 bulge''

\refer [HAN96.6] *Han, C.:  1996, {\sl Astrophys. J., submitted, Aug..96\/}, ``The Effects of Amplification Bias in Gravitational Microlensing Experiments''

\refer [HAN96.4]  Han, C., Gould, A.:  1996, {\sl Astrophys. J., Aug.96\/} {\bf  467},  540, ``Statistical determination of the MACHO mass spectrum''

\refer [HAN96.1]  Han, C., Gould, A.:  1996, {\sl Astrophys. J., Apr.96\/} {\bf  461}, 587, ``Revisit the galactic halo by pixel lensing'' 

\refer [HAN96.5]  Han, C., Gould, A.:  1996, {\sl Astrophys. J., Dec.96\/} {\bf  473}, 230, ``Galactic versus extragalactic pixel lensing events toward M31'' 

\refer [HAN96.7] *Han, C., Gould, A.:  1996, {\sl Astrophys. J., submitted, Apr.96\/}, ``Einstein radii from binary-source lensing event''

\refer [HAN96.2]  Han, C., Narayanan, V.K., Gould, A.:  1996, {\sl Astrophys. J., Apr.96\/} {\bf  461}, 587,  ``Lunar occultation of MACHOs''

\refer [HAU95.5]  Haugan, S.V.H.:  1995, {\sl Astrophys. J., submitted\/}, ``The microlensing events in Q2237+0305A: no case against small masses/large sources''

\refer [HAW96.1]  Hawkins, M.R.S.:  1996, {\sl Monthly Notices Roy. Astron. Soc., Feb.96\/}, {\bf  278},  L787, ``Dark matter from quasar microlensing''

\refer [HAW96.2]  Hawkins, M.R.S., Taylor, A.N.:  1996, {\sl Astrophys. J., submitted, Apr.96\/},  ``Quasar variability and gravitational microlensing''

\refer [HEL95.2]  Helbig, P.:  1995, {\sl Proc. of the 17th Texas Symp. on ``Relativistic Astrophysics'', in press\/}, ``Cosmological parameters and gravitational lensing statistics'' 

\refer [HEL96.1]  Helbig, P., Kayser, R.:  1996, {\sl Astron. Astrophys., Apr.96\/}  {\bf  308},  359, ``Cosmological parameters and the redshift distribution of gravitational lenses''

\refer [HEY97.1] *Heyrovsky, D., Loeb, A.:  1997, {\sl Astrophys. J., submitted, Feb.97\/}, ``Microlensing of an elliptical source by a point mass''

\refer [HOG96.1]  Hogg, D.W., Blandford, R., Kundic, T., Fassnacht, C.D., Malhotra, S.:  1996, {\sl Astrophys. J., Aug.96\/} {\bf  467}, L73,  ``A candidate gravitational lens in the Hubble Deep Field''

\refer [HOL96.1]  Holder, G.P., Widrow, L.M.:  1996, {\sl Astrophys. J., Dec.96\/} {\bf  473}, 828,  ``Microlensing by a prolate all-MACHO halo''

\refer [HOL96.1]  Holz, D.E., Wald, R.M.:  1996, {\sl Astrophys. J., Nov.96\/} {\bf  471},  64, ``Photon statistics limits for earth-based parallax measurements of MACHO events''

\refer [HOR96.1]  Horvath, J.E.:  1996, {\sl Monthly Notices Royal Astron.Soc., Feb.96\/}, {\bf 278},  L46,  ``Possible determination of isolated pulsar masses with gravitational microlensing''

\refer [IM~97.1]  Im M., Griffiths, R.E., Ratnatunga, K.U.:  1997, {\sl Astrophys. J., Feb.97\/} {\bf 475},  457, ``A measurement of the cosmological constant using elliptical galaxies as strong gravitational lenses''

\refer [IMP96.1]  Impey, C.D., Foltz, C.B., Petry, C.E., Browne, I.W.A., Patnaik, A.R.:  1996, {\sl Astrophys. J., May,1996\/} {\bf 462},  L53,  ``Hubble Space Telescope observations of the gravitational lens system B1422+231''

\refer [JAI96.1] *Jain, B., Seljak, U.:  1996, {\sl Astrophys. J., submitted, Nov.96\/},  ``Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear Regimes''

\refer [JET96.1] *Jetzer, P.,  Masso, E.:  1996,  {\sl The second workshop on ``The dark side of the Universe: experimental efforts and theoretical frameworks'' (Rome, November 1995), Jan.96\/}, ``Microlensing implications for halo dark matter''

\refer [JET95.1]  Jetzer, P., Rovetti, F., Treves, A., Urry, C.M.:  1996, {\sl Astrophys. J, submitted, Dec.95\/}, ``Microlensing in the BL Lacertae object PKS 2155-304''

\refer [JOG95.1]  Jogee, S., Kenney, J.:  1995, {\sl IAU Coll. 157, in press\/},  ``CO kinematics, star formation and dynamical evolution of the lensed starburst NGC 4102''

\refer [JON96.1]  Jones, D.L., Preston, R.A., Murphy, D.W., Jauncey, D.L., Reynolds, J.E. et al.:  1996, {\sl Astrophys. J., Oct.96\/} {\bf  470},  L23,  ``Interstellar broadening of images in the gravitational lens PKS 1830-211''

\refer [JON96.2] *Jones, M.E., Saunders, R., Baker, J.C., Cotter, G., Edge, A. et al.:  1996, {\sl Astrophys. J. Let., in press, Nov.96\/},  ``Detection of a CMB decrement towards the z = 3.8 quasar pair PC1643+4631A and B''

\refer [KAK95.1] *Kakigi, Y., Okamura, T., Fukuyama, T.: {\sl submitted\/}, ``Gravitational lensing and Catastrophe theory''

\refer [KAN96.1]  Kan-ya, Y., Nishi, R., Nakamura, T.:  1996, {\sl Publ. Astron. Soc. Japan, Jul.96\/} {\bf  48},  479, ``Microlensing and halo models of the galaxy''

\refer [KAT97.1]  Katz, C.A., Moore, C.B., Hewitt, J.N.:  1997, {\sl Astrophys. J., Feb.97\/} {\bf  475},  512, ``Multifrequency radio observations of the gravitational lens system MG 0414+0534''

\refer [KAW96.1]  Kawara, K., Murayama, T., Taniguchi, Y., Arimoto, N.:  1996, {\sl Astrophys. J., Oct.96\/} {\bf  470}, L85, ``Infrared spectroscopy of the gravitationaly lensed quasar B1422+231: Mg II $\lambda$ 2798 and Fe II emission from the broad-line gas at z=3.62''

\refer [KAI96.1] *Kaiser, N.:  1996, {\sl Astrophys. J, submitted, Oct.96\/}, ``Weak Lensing and Cosmology''

\refer [KEE96.2] *Keeton, C.R, Kochanek, C.S.:  1996, {\sl Astrophys. J, submitted, Nov.96\/}, ``Determining the Hubble Constant from the Gravitational Lens PG 1115+080''

\refer [KEE96.1] *Keeton, C.R, Kochanek, C.S., Seljak, U.:  1996, {\sl Astrophys. J, submitted, Oct.96\/}, ``Shear and Ellipticity in Gravitational Lenses''

\refer [KER96.1] *Kerins, E.J.:  1996,  {\sl  Astron. Astrophys., submitted, Oct.96\/}, `` Zero-metallicity VLM stars as halo dark matter''

\refer [KIN96.1]  King L.J., Browne I.W.A.:  1996, {\sl Monthly Notices Roy. Astron. Soc., Sep.96\/} {\bf 282},  67, ``Biases, selection effects and image multiplicities in the Jodrell Bank - VLA gravitational lens survey''

\refer [KNE96.1]  Kneib, J.-P., Ellis, R.S., Smail, I., Couch, W.J., Sharples, R.M.:  1996, {\sl Astrophys. J., Nov.96\/} {\bf  471},  643, ``Hubble Space Telescope observations of the lensing cluster Abell 2218''

\refer [KOC96.3]  Kochanek, C.S.:  1996,  {\sl  Astrophys. J., Aug.96\/} {\bf  466},  638, ``Is there a cosmological constant?''

\refer [KOC96.5] *Kochanek, C.S., Keeton, C.R.:  1996,  {\sl  Proc. of the Second Stromlo Symposium, The Nature of Elliptical Galaxies, Nov.96\/}, ``Gravitational Lensing Limits on Early-Type Galaxies''

\refer [KOC96.1]  Kochanek, C.S., Kolatt, T.S., Bartelmann, M.:  1996, {\sl  Astrophys. J., Dec.96\/} {\bf  473}, 610  ``Proper motions of VLBI lenses, inertial frames, and the evolution of peculiar velocities''

\refer [KOC96.2]  Kochanek, C.S.:  1996, {\sl Astrophys.J., Dec.96\/} {\bf  473}, 595,  ``The flat-spectrum radio luminosity function, gravitational lensing, galaxy ellipticities, and cosmology''

\refer [KOC96.4]  Kochanek, C.S., Falco, E.E., Schild, R., Dobrzycki, A., Enhels, D., Hagen, H.-J.:  1996, {\sl Astrophys.J., in press, Nov.96\/},  ``SBS 0909+532: A New Double Gravitational Lens or Binary Quasar?

\refer [KOF96.1] *Kofman, L., Kaiser, N., Lee, M.H., Babul, A.:  1996, {\sl Astrophys.J., submitted, Aug.96\/},  ``Statistics of Gravitational Microlensing Magnification. I. Two-Dimensional Lens Distribution''

\refer [KOL95.1]  Kolatt, T., Bartelman, M.:  1995, {\sl Astrophys. J., submitted, Jun.95\/}, ``Velocity dipole convergence signature from gravitational lensing''

\refer [KOL96.1]  Kolb, E.W., Tkachev, I.I.:  1996,  {\sl Astrophys. J., Mar.96\/}, {\bf  460},  L25, ``Femtolensing and picolensing by axion miniclusters''

\refer [KUN96.1] *Kundic, T., Turner, E.L., Colley, W.N., Gott, III,R., Rhoads, J.E. et al.:  1996,  {\sl Astrophys. J., submitted, Oct.96\/}, ``A Robust Determination of the Time Delay in 0957+561A,B and a Measurement of the Global Value of Hubble's Constant''

\refer [LEH96.1]  Leh{\'a}r, Cooke, A.J., Lawrence, C.R., Silber, A.d., Langston, G.I.:  1996, {\sl Astron. J., May,96\/}  {\bf 111}, 1812, ``The lensing galaxy in MG1549+3047''

\refer [LAV96.1]  Lavery, R.L.:  1996,  {\sl Astron. J., Nov.96\/} {\bf 112},  1812, ``An extremely thin gravitational arc formed by the distant cluster CL 0016+1609: Lensing of a compact HDF-type object?'' 

\refer [LEE96.1] *Lee, M.H., Babul, A., Kofman, L., Kaiser, N..:  1996,  {\sl Astrophys. J., submitted, Aug.96\/}, ``Statistics of Gravitational Microlensing Magnification. II. Three-Dimensional Lens Distribution'' 

\refer [LEH97.1] *Leh{\'a}r, J. et al.:  1997,  {\sl Astron. J., submitted, Feb.97\/}, ``The gravitationally-lensed radio source MG 0751+2716''

\refer [LEN96.1]  Lennon, D.J., Mao, S., Fuhrmann, K., Gehren, T.:  1996, {\sl Astrophys. J., Nov.96\/} {\bf  471},  L23, ``The first spectroscopic observations of caustic crossing in a binary microlensing event''

\refer [LEW95.1]  Lewis, G.F., Irwin, M.J., Hewett, P.C.:  1995, {\sl Astrophys. J., submitted, Aug.95\/}, ``Microlensing induced spectral variability in Q 2237+0305''

\refer [LIN96.1] *Linder, E.V.:  1996, {\sl submitted, Jul.96\/}, ``Correlated gravitational lensing of the CMB''

\refer [LIN97.1] *Linewear, C.H.:  1997, {\sl Proc. Int. School of Astrophys.,
"From Quantum Fluctuations to Cosmological Structures" held in Casablanca, Morocco, Dec.96\/}, ``Gold in the Doppler Hills: Cosmological Parameters in the Microwave Background''

\refer [LIU96.1]  Liu, M.C., Graham, J.M., Wright, G.S.:  1996, {\sl Astrophys. J., Oct.96\/} {\bf  470},  771, ``IRAS FSC 15307+3252: Gravitationally-Lensed Seyfert or Cannibal Elliptical at z=0.93?''

\refer [LOE97.2] *Loeb, A.:  1997, {\sl Proc. of the  Texas symposium 1996\/},  ``Gravitational Lensing of Quasars by Spiral Galaxies''

\refer [LOE97.1]  Loeb, A., Refregier, A.:  1997, {\sl Astrophys. J., Feb..97\/} {bf  476},  L55, ``Effect of gravitational lensing on measurements of the Sunyaev-Zeldovich effect''

\refer [LON96.1] *Longaretti, P.-I.:  1996, {\sl Astron. Astrophys. Let., submitted, Oct.96\/}, ``Lens reconstruction and source redshift distribution''

\refer [LOV96.1]  Lovell, J., Reynolds, J.E., Jauncey, D.L., Backus, P.R., McCulloch, P.M. et.al.:  1996, {\sl Astrophys. J., Nov.96\/} {\bf  472},  L5, `` PKS 1830-211: a possible compound gravitational lens''

\refer [LUP97.1]  Luppino, G.A., Kaiser, N.:  1997,  {\sl Astrophys. J., Jan.97\/} {\bf 475},  20, ``Detection of weak lensing by a cluster of galaxies at z=0.83''

\refer [LUP96.2]  Luppino, G.A., Kaiser, N., Clowe, D., Gioia, I.M., Metzger, M.R.:  1996,  {\sl  UCLA Dark Matter Conf., Aug.96\/}, ``Weak lensing by X-ray luminous clusters of galaxies at z > 0.5''

\refer [LUP95.1]  Luppino, G.A., Metzger, M.R., Kaiser, N., Clowe, D. et al.:  1995, {\sl  Clusters, Lensing and the Future of the Universe, submitted, Oct.95\/},  ``Observations of weak lensing in clusters with an 8192x8192 CCD mosaic camera''

\refer [MAK96.1]  Makino, N.:  1996, {\sl Publ. Astron. Soc. Japan, Sep.96\/} {\bf  48},  573, ``Structure of an X-ray cluster of galaxies with a central giant elliptical galaxy and gravitational lensing''

\refer [MAL97.1] *Maller, A.H., Flores, R.A., Primack, J.R.:  1997,  {\sl Astrophys. J., submitted, Jan.97\/}, ``Inclination effects in spiral galaxy gravitational lensing''

\refer [MAL96.1] *Malhotra, S., Rhoads, J.E., Turner, E.L.:  1996, {\sl Monthly Notices Roy. Astron. Soc., submitted, Oct.1996\/},  ``Through a Lens Darkly: Evidence for Dusty Gravitational Lenses''

\refer [MAO96.1]  Mao, S., Paczy{\'n}ski, B.:  1996, {\sl Astrophys. J., Dec.96\/} {\bf  473},  57, ``Mass determination with gravitational microlensing''

\refer [MAO96.2] *Maoz, D., Rix, H.-W. Rix, Gal-Yam, A., Gould, A.:  1996,  {\sl  Astrophys. J., Dec.96\/}, ``A survey for large image-separation lensed quasars''

\refer [MAR96.1] *Markovic, D., Sommer-Larsen, J.:  1996, {\sl Monthly Notices Roy. Astron. Soc., submitted, Sep.1996\/},  ``Microlensing, structure of the galactic halo and determination of dark objects' mass function''

\refer [MAR97.1] *Martinez-Gonz{\'a}lez, E., Sanz, J.L., Cay{\'o}n, L.:  1997, {\sl Astrophys. J., submitted, Feb.97\/},  ``The effect of weak gravitationallensing on the cosmic microwave background anisotropy: flat versus open universe''

\refer [MAS97.1] *Mathur, S., Nair, S.:  1997, {\sl Astrophys. J., to appear Jul.20\/} {\bf  484}, ``X-ray Absorption Towards The Einstein Ring Source PKS1830-211''

\refer [MAS96.1] *Masso, E.:  1996, {\sl  IV Workshop on Theoretical and Phenomenological Aspects of Underground Physics, TAUP95, Toledo (Spain), Sept. 17-21, Jan.96\/},  ``Baryonic Dark Matter: Theory and Experiment. Overview''

\refer [MEL96.1] *Mellier, Y., Fort, B.: 1996, {\sl ESO Workshop on "The Early Universe with the VLT", Apr.96\/}, ``Weak lensing at the limit of the sky background noise''

\refer [MEL96.2] *Mellier, Y.: 1996, {\sl 37th Herstmonceux Conference on "HST
  and the High Redshift Universe" 1-5 july 1996\/}, ``Gravitational Lensing and the Redshift Distribution of $B>25$ galaxies''

\refer [MEL96.3] *Mellier, Y., van Waerbeke, L., Bernardeau, F., Fort, B.: 1996, {\sl Invited talk for the VIIIth Rencontres de Blois, "Neutrinos, Dark
  Matter and the Universe" 6-12 Jun.96\/},  ``Recent Advances in Gravitational Lensing''

\refer [MEN96.1]  Menten, K.M., Reid, M.J.: 1996, {\sl Astrophys. J., Jun.96\/}
{\bf 465},  L99, ``Formaldehyde Absorption at z = 0.685 toward the Einstein Ring B0218+357''

\refer [MET96.1]  Metcalf, R.B., Silk, J.:  1996, {\sl Astrophys.J., Jun.96\/} {\bf  464}, 218, ``Gravitational microlensing by clustered MACHOs''

\refer [MIC96.2]  Michalitsianos, A.G., Oliversen, R.J., Nichols, J.:  1996,  {\sl Astrophys. J., Apr.96\/} {\bf  461},  593, ``Detection of OVI $\lambda$ 1033 emission and far-ultraviolet spectral variability in the gravitational lens PG1115+080''

\refer [MIC96.1]  Michalitsianos, A.G., Oliversen, R.J., Maran, S.P.:  1996,  {\sl Astrophys. J., Feb.96\/}, {\bf  458},  67, ``Far-UV spectral variability in the gravitational lens candidate UM 425''

\refer [MIC97.1]  Michalitsianos, A.G., Dolan, J.F., Kazanas, D., Bruhweiler, F.C., Boyd, P.T. et al.:  1996,  {\sl Astrophys. J., Jan.97\/} {\bf  474},  598,  ``Ly $\alpha$ Absorption Line Systems in the Gravitational Lens Q0957+561''

\refer [MIR96.1]  Miralda-Escud{\'e}, J.:  1996, {\sl Astrophys. J., Oct.96\/} {\bf  470},  L113,  ``Microlensing events from measurements of the deflection''

\refer [MOH95.1] *Mohanty, S., Prasanna, A.R.:  1995, {\sl submitted\/},  ``No birefringence in Einstein's gravity''

\refer [MOL96.1]  Mollerach, S., Roulet, E.:  1996, {\sl Astrophys. J., Feb.96\/}, {\bf  458},  L9, ``Microlensing of disk source''

\refer [MOL96.2]  Mollerach, S., Roulet, E.:  1996, {\sl Astrophys. J., submitted, Sep.96\/}, ``Kicked neutron stars and microlensing''

\refer [MON96.1]  Montoya, M.L., Dominguez-Tenreiro, R., Gonz{\'a}lez-Casado, G.,  Mamon, G.A., Salvador-Sol{\'e}, E.:  1996, {\sl Astrophys. J., Dec.96\/} {\bf 473},  L83, ``The surface density profiles and lensing characteristics of Hickson compact groups of galaxies''

\refer [MUN95.1]  Munoz, J.A., Portilla, M.:  1995, {\sl Astrophys. J., submitted\/}, ``Effect of large scale inhomogeneities on the relative deviation of the two light rays''

\refer [MUN96.1]  Munoz, J.A., Portilla, M.:  1996, {\sl Astrophys. J., Jul.96\/} {\bf  465},   562, ``Light deflection by large scale structure and cosmic microwave background''

\refer [NAI97.1]  Nair, S., Garret, M.A.:  1997, {\sl Monthly Notices Roy.Astron.Soc., Jan.97\/} {\bf  284},  58, ``Gravitational lens model for 2016+112''

\refer [NAK96.1] *Nakamura, T., Suto, Y.:  1996,  {\sl  Prog. of Theoretical Physics, in press, Dec.96}, ``Strong Gravitational Lensing and Velocity Function as Tools to Probe Cosmological Parameters: Current Constraints and Future Predictions''

\refer [NAK96.2]  Nakamura, T.T., Kan-ya, Y., Nishi, R.:  1996, {\sl Astrophys. J., Dec.96\/} {\bf  473},  L99, ``The Minimum Total Mass of MACHOs and Halo Models of the Galaxy''

\refer [NAR96.1] *Narayan, R., Bartelmann, M.:  1996, {\sl Lectures held at the 1995 Jerusalem Winter School, Jun.96\/}, ``Lectures on Gravitational Lensing''

\refer [NAT95.1] *Natarajan, P.:  1995 {\sl Astrophys. J., submitted, Sep.95\/}, ``Study of the dynamics of the core of A2218''

\refer [NAT95.2] *Natarajan, P., Kneib J.-P.:  1995, {\sl submitted\/}, ``Effect of sub-structure in clusters on the local weak-shear field''

\refer [NAT96.1]  Natarajan, P., Kneib J.-P.:  1996, {\sl Monthly Notices Roy.Astron.Soc., Dec.96\/} {\bf  283},  1031, ``Probing the dynamics of cluster-lenses''

\refer [NAT96.2] *Natarajan, P., Lynden-Bell, D.:  1996, {\sl Monthly Notices Roy.Astron.Soc., in press, Sep.96\/}, ``An analytic approximation to the isothermal sphere''

\refer [NEM97.1]  Nemiroff, R.J.:  1997,  {\sl Astrophys. J., submitted, Jan.97\/}, ``Bright lenses and optical depth''

\refer [NEU96.1] *Neumann, D.M., Boehringer, H.:  1996, {\sl Monthly Notices Roy.Astron.Soc., submitted, Jul.96\/}, ``X-ray properties of the distant cluster Cl0016+16''

\refer [NIK97.1] *Nikolaev, S., Weinberg, M.D.:  1997,  {\sl Astrophys. J., submitted, Jan.97\/}, ``A rigorous reanalysis of the IRAS variable population: scale lengths, asymmetries, and microlensing''

\refer [OMO96.1] *Omont, A.,  Petitjean, P., Guilloteau, S., McMahon, R.G., Solomon, P.M., Pecontal, E.:  1996, {\sl submitted, Aug.96\/} ``Molecular gas and dust around a radio-quiet quasar at redshift 4.7''

\refer [OSC96.1]  Oscoz, A., Serra-Ricart, M., Goicoechea, L.-J., Buitrago, J., Mediavilla, E.:  1996, {\sl Astrophys. J., Oct.96\/} {\bf  470},  L19,  ``Optical photometry of quasar 0957+561A,B''

\refer [OSC97.1]  Oscoz, A., Mediavilla, E., Goicoechea, L.-J., Serra-Ricart, M., Buitrago, J.:  1997, {\sl Astrophys. J., Apr.97\/} {\bf  479},  L89,  ``Time delay of QSO 0957+561 and cosmological implications''

\refer [OST96.1]  Ostensen, R., Refsdal, S., Stabell, R., Teuber, J., Emanuelsen, P.I. et al.:  1996, {\sl Astron. Astrophys., May,96\/} {\bf  309}, 59, ``Monitoring of the Einstein Cross with the Nordic Optical Telescope''  

\refer [OST97.1]  Ostensen, R., Remy, M., Lindblad, P.O., Refsdal, S., Stabell, R. et al.:  1997, {\sl Astron. Astrophys., in press, Mar.97\/}, ``ESO and NOT photometric monitoring of the Cloverleaf quasar''  

\refer [PAC95.4]  Paczy{\'n}ski, B.:  1995, {\sl submitted, Oct.95\/}, ``Gravitational microlensing, the distance scale, and the ages''

\refer [PAC95.5]  Paczy{\'n}ski, B.:  1995, {\sl submitted\/}, ``The masses of nearby dwarfs can be determined with gravitational microlensing''

\refer [PAC96.1] *Paczy{\'n}ski, B.:  1996, {\sl submitted, Apr.96\/}, ``Gravitational Microlensing in the Local Group''

\refer [PAC96.2] *Paczy{\'n}ski, B.:  1996, {\sl Acta Astronomica, submitted, Jun.96\/}, ``The Masses of Nearby Dwarfs and Brown Dwarfs with the HST''

\refer [PAR96.1] *Park, M.-G.:  1996,{\sl J. Kor. Phys. Soc., in press, Sep.96\/}, ``Gravitational Lensing Statistics in a Flat Universe''

\refer [PAR97.1] *Park, M.-G., Gott III, J.R.:  1997,  {\sl Astrophys. J., submitted, Feb.97\/}, ``Curvature of the universe and observed gravitational lens image separations versus redshift''

\refer [PAT96.1]  Patnaik, A., Schneider, P., Narayan, R.:  1996,  {\sl Monthly Notices Roy. Astron. Soc., Jul.96\/} {\bf  281}, L17,  ``A deep radio observation of the gravitational lens candidate QSO 2345+007''

\refer [PEA96.1] *Peale, J.S.:  1996, {\sl Icarus, submitted, Oct.96\/}, ``Expectations from a microlensing search for planets''

\refer [PEL96.1] *Pello, R.,  Miralles, J.M., Le Borgne, J.-F., Picat, J.-P., Soucail, G., Bruzual, G.:  1996, {\sl Astron. Astrophys., in press, May,1996\/},
 ``Identification of a high redshift cluster in the field of Q2345+007 through deep BRIJK' photometry''

\refer [PEL96.1]  Pelt, J., Kayser, R., Refsdal, S., Schramm, T.:  1996, {\sl Astron. Astrophys., Jan.96\/}, {\bf  305},  97, ``The light curve and the time delay of QSO 0957+561''

\refer [PEN97.1]  Peng, E.W.:  1997, {\sl  Astrophys. J., Jan.97\/} {\bf 475}, 43,  ``The feasibility of obtaining finite source sizes from MACHO-type microlensing light curves''

\refer [PER96.1]  Perna, R., Loeb, A., Bartelmann, M.:  1996, {\sl  Astrophys. J., submitted, Jul.96\/}, ``Effects of dust on gravitational lensing by spiral galaxies''

\refer [PER97.1] *Perna, R., Loeb, A.:  1997, {\sl  Astrophys. J., submitted, Jan.97\/}, ``Microlensing of quasars by stars in their damped Ly $\alpha$ absorbers''

\refer [PET96.1]  Petters, A.O., Witt, H.J.:  1996,  {\sl J. Math. Phys., submitted, Jan.96\/},  ``Bounds on numbers of cusps due to point mass gravitational lenses''

\refer [PIE96.1]  Pierre, M., Le Borgne, J.F., Soucail, G., Kneib, J.P.:  1996, {\sl Astron. Astrophys., Jul.96\/}, {\bf  311},  413, ``X ray analysis and matter distribution in the lens-cluster Abell 2390''

\refer [PIJ96.1] *Pijpers, F.P.:  1996,  {\sl Monthly Notices Roy. Astron. Soc., submitted, Jul.96\/}, ``The determination of time lags using SOLA''

\refer [PRA96.1] *Pratt, M.R., Alcock, C., Allsman, R.A., Alves, D., Axelrod, T.S. et al.:  1996, {\sl Proc. "Sources and Detection of Dark Matter in the Universe", Santa Monica, CA, Feb., 1996\/}, ``The MACHO Project 2nd Year LMC Microlensing Results and Dark Matter Implications''

\refer [PRI95.1] *Primack, J.R.:  1995, {\sl Plenary talk at Snowmass, 1994\/}, ``Status of cosmological parameters: can $\Omega=1$?''

\refer [PYN96.1]  Pyne, T., Birkinshaw, M.:  1995, {\sl Astrophys. J., Feb.96\/}, {\bf  458},  46, ``Beyond the thin lens approximation''

\refer [PYN95.2] *Pyne, T., Carroll, S.M.:  1995, {\sl submitted, Oct.95\/}, ``Higher-Order Gravitational Perturbations of the Cosmic Microwave Background''

\refer [PYN96.2]  Pyne, T., Gwinn, C.R., Birkinshaw, M., Eubanks, T.M., Matsakis, D.N.:  1996, {\sl Astrophys. J., Jul.96\/} {\bf  465}, 566,  ``Gravitational radiation and very long baseline interferometry''

\refer [QIN96.1] *Qin, B., Wu, X.-P., Zou, Z.:  1996, {\sl submitted, Nov.96\/}, ``Self-Microlensing in Compact Binary Systems''

\refer [RAD95.1]  Radford, S.J.E., Downes, D., Solomon, P.M., Barrett, J., Sage, L.J.:  1995, {\sl Astron. J., in press\/}, ``Resolution of the discrepancy in the CO(3-2) flux of IRAS F10214+4724''  

\refer [REF95.1] *Refregier, A., Loeb, A.:  1995, {\sl Proc. of "Rontgenstrahlung from the Universe" 1995, in press\/}, ``Probing cluster potentials through gravitational lensing of background X-ray sources''

\refer [REF97.1]  Refregier, A., Loeb, A.:  {\sl Astrophys. J., Apr.97\/}  {\bf  478}, 476, ``Gravitational Lensing of the X-Ray Background by Clusters of Galaxies''

\refer [REG96.1]  Regos, E.:  1996, {\sl Astron. Astrophys., Apr.96\/}  {\bf  308}, 368, ``An unbiased value of $\Omega$ from cluster infall and gravitational lensing''

\refer [REN96.1] *Renault, C., Afonso, C., Aubourg, E., Bareyre, P., Bauer, F., (EROS collaboration):  1996,  {\sl Astron. Astrophys., submitted, Dec.96\/},
``Observational Limits on Machos in the Galactic Halo''

\refer [RHI95.1] *Rhie, S.H.:  1995, {\sl Astrophys. J., submitted, Aug.95\/}, ``Infimum microlensing amplification of the maximum number of images of $n$-point lens systems''

\refer [RHI96.1] *Rhie, S.H., Bennet, D.P.:  1996, {\sl Proc. Second International Symposium on Sources and Detection of Dark Matter in the Universe,1996\/}, ``Search for Earth-Mass Planets and Dark Matter, Too''

\refer [RHO96.1]  Rhoads, J.E., Malhotra, S., Kundic, S.:  1996, {\sl Astron. J., Feb.96\/}, {\bf  111},  642, `` Infrared counterpart of the gravitational lens 1938+66.6''

\refer [RIO97.1]  Rioja, M.J., Marcaide, J.M., Elosegui, P., Shapiro, I.I.:  1997,  {\sl Astron. Astrophys., accepted, Mar.97\/},``Results from a decade-long VLBI astrometric monitoring of the pair of quasars 1038+528 A and B''

\refer [ROU96.1] *Roulet, E., Mollerach, E.:  1996, {\sl Physics Reports, in press, Mar.96\/}, ``Microlensing''

\refer [SAM96.1]  Sams III, B.J., Schuster, K., Brandl, B.:  1996, {\sl Astrophys. J., Mar.96\/} {\bf  459}, 491, ``A search for molecular gas in high-redshift normal galaxies in the foreground of the gravitationally lensed quasar Q1208+1011''

\refer [SAR96.1]  Saraniti, D.W., Pretrosian, V., Lynds, R.:  1996, {\sl Astrophys. J., Feb.96\/} {\bf  458},  57, ``Gravitational lens model of arcs in Abell 2218''

\refer [SAR96.2]  Sari, S.:  1996, {\sl Astrophys. J., May,96\/} {\bf  462}, 110, ``Gravitational deflection of light by a rotating astrophysical object''

\refer [SAS97.1] *Sasselov, D.D.:  1997, {\sl 12th IAP Colloquium on "The Astrophysical Returns of Microlensing Surveys", eds. R.Ferlet and J.P.Maillard, Feb.97\/}, ``The Chromaticity of Microlensing (Surface Imaging of Stars)''

\refer [SAU96.3] *Saunders, R.:  1996, {\sl Proc. of the XXXIst Rencontre de Moriond, `Microwave Background Anisotropies', Nov.96\/}, ``Sunyaev-Zel'dovich observations with the Ryle Telescope''

\refer [SAU96.2] *Saunders, R., Baker, J.C, Bremer, M.N., Bunker, A.J., Cotter, G. et al.:  1996, {\sl Astrophys. J. Let., Nov.96\/}, ``Optical and infrared investigation towards the z=3.8 quasar pair PC1643+4631A and B''

\refer [SAU96.1] *Saust, A.B.:  1996, {\sl Astrophys. J., submitted, Jul.96\/}, ``A statistical investigation of the contamination of binary gravitational lens candidates by cataclysmic variables'' 

\refer [SCH97.3]  Schechter, P.L., Bailyn, C.D., Barr, R., Barvainis, R., Becker, C.M. et al.:  1997, {\sl Astrophys. J., Feb.97\/} {\bf  475}, L85, ``The quadruple gravitational lens PG 1115+080: Time delays and models''

\refer [SCH96.4]  Schild, R.:  1996, {\sl Astrophys. J., Jun.96\/} {\bf  464},  125, ``Microlensing variability of the gravitationally lensed quasar Q0957+561A,B''

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\refer [SCH95.6] *Schneider, P.:  1995, {\sl Proceedings of the Laredo Advanced Summer School, Sept. 95\/}, `` Cosmological applications of gravitational lensing''

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\refer [SEI96.3] *Seitz, C., Schneider, P.:  1996, {\sl Astron. Astrophys., in press, Jan.96\/}, ``Steps towards nonlinear cluster inversion through gravitational distortions: III. Including a redshift distribution of the sources''

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\endrefer

\newpage

\noindent {\Large \bf Abstracts of articles whose first author is marked 
with a $\star$ among submitted papers and articles in press}\\

%\vs

\par


Paper: astro-ph/9609165
From: alard@iap.fr (Christophe Alard)
Date: Tue, 24 Sep 96 19:42:11 +0200

Title: Lensing of unresolved stars towards the Galactic Bulge
Author: C. Alard (DEMIRM and CAI, Obs. de Paris)
Comments: 12 pages LaTeX with l-aa.sty and psfig.sty. Accepted for publication
  in Astronomy and Astrophysics
Report-no: MAMA-9
\\
  Previous calculations of the rates and optical depths due to microlensing
only considered resolved stars. However, if a faint unresolved star lens is
close enough to a resolved star, the event will be seen by the microlensing
experiments and attributed to the bighter star. The blending biases the
duration, making the contribution of the unresolved stars very significant for
short events. This contribution is confused with lensing by brown dwarfs. The
exact rates of these blended events are extremly sensitive to the limiting
magnitude achieved in the microlensing search. Appropriate calculations of the
optical depth and rates are provided here, and illustrated in the case of the
DUO and OGLE experiments. The additional contribution of unresolved stars is
very significant and probably explains the high optical depth and rates
observed towards the Galactic Bulge. The blended unresolved event can be
identified using either the color shift or the light curve shape. However,
neither of these two methods is apropriate to identify a large number of
blended events towards the Bulge. In some cases of good photometry and small
impact parameter, an identification is possible, as for the OGLE 5 event, which
clearly appears as a case of lensing of an unresolved star. The recent results
obtained by the PLANET collaboration indicate that a high resolution and dense
sampling of the light curve is possible, and will probably provide a very
interesting possibility to correct the blending bias, as demonstrated for OGLE
5. This possibility, is certainly better than a statistical estimation of the
lensing rates, which are always prone to some uncertainty. But, at this time,
the contribution of unresolved stars must be included in the analyses of
microlensing experiments.
 (http://xxx.lanl.gov/abs/astro-ph/9609165 ,  84kb)
\\


Paper: astro-ph/9610128
From: Penny D. Sackett psackett@astro.rug.nl
Date: Wed, 16 Oct 1996 11:24:53 MDT

Title: The Planet Collaboration: Probing Lensing Anomalies
Authors:  The PLANET Collaboration: M. Albrow, J.-P. Beaulieu, P. Birch,
  J.A.R. Caldwell, J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies,
  R.M. Naber, J.-W. Pel, K. Pollard, P.D. Sackett, K.C. Sahu, P. Vreeswijk,
  R. Watson, A. Williams, M. Zwaan
Comments: LaTex (using conf\_iap.sty) 5 pages with 5 figures, the two large
  figures Fig. 3 and Fig. 5b are in .gif format. To appear in the Proceeedings
  of the 12th IAP Conference: Variable Stars and the Astrophysical Returns of
  Microlensing Surveys
\\
  The Probing Lensing Anomalies NETwork (PLANET) is a worldwide collaboration
of astronomers using semi-dedicated European, South African, and Australian
telescopes to perform continuous, rapid and precise multi-band CCD photometric
monitoring of on-going Galactic microlensing events. As well as providing
important additional information on the nature, distribution and kinematics of
Galactic microlenses, PLANET photometry is optimized for the detection of
Jovian-mass planets orbiting several AU from Galactic lenses. The final PLANET
database is expected to contain hundreds of variable stars sampled at hourly
time scales with 1-5% precision.
 (http://xxx.lanl.gov/abs/astro-ph/9610128 ,  109kb)
\\


Paper: astro-ph/9702199
From: Andrew Becker 

becker@lensing.astro.washington.edu
Date: Sat, 22 Feb 1997 13:56:50 -0800   (281kb)

Title: MACHO Alert 95-30 : First Real-Time Observation of Extended Source
  Effects in Gravitational Microlensing
Authors: C.Alcock, W.H.Allen, R.A.Allsman, D.Alves, T.S.Axelrod, T.S.Banks,
  S.F.Beaulieu, A.C.Becker, R.H.Becker, D.P.Bennett, I.A.Bond, B.S.Carter,
  K.H.Cook, R.J.Dodd, K.C.Freeman, M.Gregg, K.Griest, J.B.Hearnshaw, A.Heller,
  M.Honda, J.Jugaku, S.Kabe, S.Kaspi, P.M.Kilmartin, A.Kitamura, O.Kovo,
  M.J.Lehner, T.E.Love, D.Maoz, S.L.Marshall, Y.Matsubara, D.Minniti,
  M.Miyamoto, Y.Muraki, T.Nakamura, B.A.Peterson, M.R.Pratt, P.J.Quinn,
  I.N.Reid, M.Reid, D.Reiss, A.Retter, A.W.Rodgers, W.L.W.Sargent, H.Sato,
  M.Sekiguchi, P.B.Stetson, C.W.Stubbs, D.J.Sullivan, W.Sutherland, A.Tomaney,
  T.Vandehei, Y.Watase, D.L.Welch, T.Yanagisawa, M.Yoshizawa, P.C.M.Yock
Comments: 32 pages including 6 tables, and 15 figures; Uses AASTeX 4.0;
  submitted to The Astrophysical Journal
\\
  We present analysis of MACHO Alert 95-30, a dramatic gravitational
microlensing event towards the Galactic bulge whose peak magnification departs
significantly from the standard point-source microlensing model. Alert 95-30
was observed in real-time by the Global Microlensing Alert Network (GMAN),
which obtained densely sampled photometric and spectroscopic data throughout
the event. We interpret the light-curve ``fine structure'' as indicating
transit of the lens across the extended face of the source star. This signifies
resolution of a star several kpc distant. We find a lens angular impact
parameter$ \theta_{min}/\theta_{source} = 0.715 \pm 0.003$. This 
information, along
with the radius and distance of the source, provides an additional constraint
on the lensing system. Spectroscopic and photometric data indicate the source
is an M4 III star of radius 61 +/- 12 Rsun, located on the far side of the
bulge at 9 kpc. We derive a lens angular velocity, relative to the source, of
21.5 +/- 4.9 km/s/kpc, where the error is dominated by uncertainty in the
source radius. Likelihood analysis yields a median lens mass of
0.67{+2.53}{-0.46} Msun, located with 80% probability in the Galactic bulge at
a distance of 6.93{+1.56}{-2.25} kpc. If the lens is a main-sequence star, we
can include constraints on the lens luminosity. This modifies our estimates to
$M_lens$ = 0.53{+0.52}{-0.35} Msun and $D_lens$ = 6.57{+0.99}{-2.25} kpc. Spectra
taken during the event show that the absorption line equivalent widths of H
alpha and the TiO bands near 6700 A vary, as predicted for microlensing of an
extended source. This is most likely due to center-to-limb variation in the
stellar spectral lines. These data demonstrate the feasibility of using
microlensing limb crossings as a tool to probe stellar atmospheres directly.
 ( http://xxx.lanl.gov/abs/astro-ph/9702199 ,  281kb)
\\


Paper: astro-ph/9606165
From: Will Sutherland 

w.sutherland1@physics.oxford.ac.uk
Date: Wed, 26 Jun 1996 18:59:14 +0100 (BST)

Title: THE MACHO PROJECT LMC MICROLENSING RESULTS FROM THE FIRST TWO YEARS AND THE NATURE OF THE GALACTIC DARK HALO
Authors: C. Alcock, R.A. Allsman, D. Alves, T.S. Axelrod, A.C. Becker, D.P.
  Bennett, K.H. Cook, K.C. Freeman, K. Griest, J. Guern, M.J. Lehner, S.L.
  Marshall, B.A. Peterson, M.R. Pratt, P.J. Quinn, A.W. Rodgers, C.W. Stubbs,
  W. Sutherland, D.L. Welch (The MACHO Collaboration)
Comments: Latex, 54 pages, uses aas2pp4.sty and astrobib.sty, with 24 out of 26
  Postscript figures in gzipped tar file. 2 extra greyscale figures and/or full
  paper available from ftp://igpp.llnl.gov/pub/macho/LMC2/ Submitted to ApJ,
  June 1996
\\
  The MACHO Project is a search for dark matter in the form of massive compact
halo objects (Machos). Photometric monitoring of millions of stars in the Large
Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic bulge is
used to search for gravitational microlensing events caused by these otherwise
invisible objects. Analysis of the first 2.1 years of photometry of 8.5 million
stars in the LMC reveals 8 candidate microlensing events. This is substantially
more than the number expected ($\sim 1.1$) from lensing by known stellar
populations. The timescales Ts of the events range from 34 to 145 days.
We estimate the total microlensing optical depth towards the LMC from events
with $2 < Ts < 200$ days to be $\tau_2^{200} = 2.9 ^{+1.4}_{-0.9} 10**{-7}$
based upon our 8 event sample. This exceeds the optical depth, $\tau_{\rm
backgnd} = 0.5 10**{-7}$, expected from known stars, and the difference is to
be compared with the optical depth predicted for a ``standard" halo composed
entirely of Machos: $\tau_{halo} = 4.7 10**{-7}$. Likelihood analysis gives a
fairly model independent estimate of the halo mass in Machos within 50 kpc of
$2.0^{+1.2}_{-0.7} 10**{11} M_{odot}$, about half of the ``standard halo" value.
We also find a most probable Macho mass of $0.5^{+0.3}_{-0.2}M_{odot}$, although
this value is strongly model dependent. Additionally, the absence of short
duration events places stringent upper limits on the contribution of low-mass
Machos: objects from $10^{-4} M_{odot}$ to $0.03 M_{odot}$ contribute $\simeq 20\%$
of the ``standard" dark halo.
 (http://xxx.lanl.gov/abs/astro-ph/9606165 ,  793kb)
\\


Paper: astro-ph/9502102
From: kaplan@lpthe.jussieu.fr (Jean KAPLAN)
Date: Mon, 27 Feb 1995 18:19:31 +0100 (MET)

Title: AGAPE, AN EXPERIMENT TO DETECT MACHO's IN THE DIRECTION OF THE ANDROMEDA GALAXY
Authors: R. Ansari, M. Auri\'ere, P. Baillon, A. Bouquet, G. Coupinot, C.
  Coutures, C. Ghesqui\`ere, Y. Giraud-H\'eraud, P. Gondolo, J. Hecquet, J.
  Kaplan, A.L. Melchior, M. Moniez, J.P. Picat and G. Soucail
Comments: 4 pages, 1 figure in a separate compressed, tarred, uuencoded uufile.
  In case ofproblem contact kaplan@lpthe.jussieu.fr
Report-no: PAR-LPTHE 95-07
\\
The status of the Agape experiment to detect Machos in the direction of the
andromeda galaxy is presented.
\\


Paper: astro-ph/9602015
From: Jean Kaplan kaplan@cdf.in2p3.fr
Date: Fri, 2 Feb 1996 19:46:45 +0100 (MET)

Title: AGAPE, A MICROLENSING SEARCH IN THE DIRECTION OF M31: STATUS REPORT
Authors: R. Ansari, M. Auriere, P. Baillon, A. Bouquet, G. Coupinot, C.
  Coutures, C. Ghesquiere, Y. Giraud-Heraud, P. Gondolo, J. Hecquet, J. Kaplan,
  Y. Le Du, A.L. Melchior, M. Moniez, J.P. Picat, and G. Soucail
Comments: 5 pages, Latex2e, includes 5 figures, uuencoded gziped tar file.
  Proceedings of the workshop ``The dark side of the Universe : experimental
  efforts and theoretical framework'' Roma 13-14 November 1995
Report-no: LPC 96-04/conf
\\
  A status report of the microlensing search by the pixel method in the
direction of M31, on the 2 meter telescope at Pic du Midi is given. Pixels are
stable to a level better than 0.5%. Pixel variations as small as 0.02 magnitude
can clearly be detected.(http://xxx.lanl.gov/abs/astro-ph/9602015 ,  122kb)
\\


Paper: astro-ph/9607040
From: Jean Kaplan kaplan@cdfas2.in2p3.fr
Date: Sat, 6 Jul 1996 12:55:46 MDT

Title: AGAPE: A SEARCH FOR DARK MATTER TOWARDS M31 BY MICROLENSING EFFECTS ON UNRESOLVED STARS
Authors: R. Ansari, M. Auri\`ere, P. Baillon, A. Bouquet, G. Coupinot, Ch.
  Coutures, C. Ghesqui\`ere,Y. Giraud-H\'eraud, P. Gondolo, J. Hecquet, J.
  Kaplan, Y. Le Du, A.L. Melchior, M. Moniez, J.P. Picat, G. Soucail
Comments: 13 pages, 15 figures, tex source and figure in one uuencoded gziped
  tar archive. Text and figures with better definition will also be available
  at http://cdfinfo.in2p3.fr/Experiences/AGAPE/publis.html
Report-no: LPC 96 33
\\
  M31 is a very tempting target for a microlensing search of compact objects in
galactic haloes. It is the nearest large galaxy, it probably has its own dark
halo, and its tilted position with respect to the line of sight provides an
unmistakable signature of microlensing. However most stars of M31 are not
resolved and one has to use the ``pixel method'': monitor the pixels of the
image rather than the stars. AGAPE is the implementation of this idea. Data
have been collected and treated during two autumns of observation at the 2
metre telescope of Pic du Midi. The process of geometric and photometric
alignment, which must be performed before constructing pixel light curves, is
described. Seeing variations are minimised by working with large super-pixels
($2.1 "$) compared with the average seeing. A high level of stability of pixel
fluxes, crucial to the approach, is reached. Fluctuations of super-pixels do
not exceed 1.7 times the photon noise which is 0.1\% of the intensity for the
brightest ones. With such stable data, 10 microlensing events are expected for
a full ``standard halo''. With a larger field, a regular and short time
sampling and a long lever arm in time, the pixel method will be a very
efficient tool to explore the halo of M31.
(http://xxx.lanl.gov/abs/astro-ph/9607040 ,  363kb)
Paper: astro-ph/9607040
replaced with revised version Tue, 10 Dec 1996 10:23:35 MST

Title: AGAPE: a search for dark matter towards M31 by microlensing effects on
  unresolved stars
Authors: R. Ansari, M. Auri\`ere, P. Baillon, A. Bouquet, G. Coupinot, Ch.
  Coutures, C. Ghesqui\`ere,Y. Giraud-H\'eraud, P. Gondolo, J. Hecquet, J.
  Kaplan, Y. Le Du, A.L. Melchior, M. Moniez, J.P. Picat, G. Soucail
Comments: 15 pages, 15 figures. Text and figures with better definition will
  also be available at http://cdfinfo.in2p3.fr/Experiences/AGAPE/publis.html
  Modified according to the requirement of the referee. To appear in A and A
Report-no: LPC 96 33
 (http://xxx.lanl.gov/abs/astro-ph/9607040 ,  557kb)
\\


Paper: astro-ph/9611110
From: asada@vega.ess.sci.osaka-u.ac.jp (Hideki Asada)
Date: Thu, 14 Nov 96 11:44:33 JST

Title: Critical Lines in Gravitational Lenses and the Determination of
  Cosmological Parameters
Authors: Hideki Asada (Osaka U.)
Comments: 16 pages, LaTeX(aaspp4), 11 postscript figures included; submitted to
  The Astrophysical Journal
Report-no: OU-TAP-49
\\
  We investigate the cosmological test recently proposed by B. Fort, Y. Mellier
and M. Dantel-Fort (FMD), where the observed location of the critical line in
gravitational lensing is used to determine the cosmological parameters,
$\Omega$ and $\lambda$. Applying this method to the cluster of galaxies
Cl0024+1654, FMD obtained a constraint on the cosmological constant, $\lambda >
0.6$, assuming the spatially flat universe. It plays a crucial role in this
method that the angular diameter distance-redshift relation depends on the
cosmological models through the cosmological parameters. First, using the
angular diameter distance in the Friedmann-Lemaitre- Robertson-Walker universe,
we show that one can hardly determine $\Omega$ by this method without the
assumption of the spatially flat universe. We also investigate the effect of
inhomogeneities of the universe by using the Dyer-Roeder angular diameter
distance. It is shown that the effect of inhomogeneities can become too large
to be ignored, particularly for a high density universe. As a result, this
method cannot be taken as a clear cosmological test to determine $\Omega$ and
$\lambda$, though it may provide a bound on $\Omega$ and $\lambda$. Moreover,
we mention the uncertainty of the determination of the velocity dispersion,
which is regarded as one of the most serious problems in this test.
 (http://xxx.lanl.gov/abs/astro-ph/9611110 ,  105kb)
\\


Paper: astro-ph/9608061
From: KATSUAKI ASANO 

sph10001@bkc.ritsumei.ac.jp
Date: Mon, 12 Aug 1996 17:18:20 +0900

Title: Elliptical lens model in PG1115+080
Authors: K.Asano and T.Fukuyama (Ritsumeikan Univ.)
Comments: 12pages, Latex, 10 tables as Postscript file, 3 PostScript Figures
Report-no: Ritsumei-pp-12
\\
  Using the new observational data, the elliptical lens model with softened
power law behaviour has been applied to the multiple quasar PG1115+080. Our
result shows that the lensing object is not compact contrary to the result by
Narashimaha et al. Core radius ranges $3 \sim 5 Kpc \cdot h^{-1}$ and total
mass is roughly $10^{12} M_{\odot}$. Central density $\rho_0 \simeq 10^{-23}
h^2 g/cm^3$, which is 10 times larger than the density of the standard galaxy.
The numerical results and their discrepancies with the observations are
discussed, especially, in comparison with the multipole expansion model.
 (http://xxx.lanl.gov/abs/astro-ph/9608061 ,  85kb)
\\


Paper: astro-ph/9508107
From: tsa@merlin.anu.edu.au (Tim Axelrod)
Date: Thu, 24 Aug 1995 15:59:08 +1000

Title: THE MACHO DATA PIPELINE
Author: T. S. Axelrod (MSSSO and LLNL), R. A. Allsman (ANUSF), P. J. Quinn
  (ESO), D. P. Bennett (CfPA), K. C. Freeman, B.A. Peterson, A. W. Rodgers
  (MSSSO), C. Alcock, K. H. Cook (LLNL), K. Griest (UCSD), S. L. Marshall, M.
  R. Pratt, C. W. Stubbs (UW), and W. Sutherland (Oxford)
Comments: 36 pages, 6 Postscript figures, uuencoded compressed tar. Submitted
  to PASP
\\
  The MACHO experiment is searching for dark matter in the halo of the Galaxy
by monitoring more than 20 million stars in the LMC and Galactic bulge for
gravitational microlensing events. The hardware consists of a 50 inch
telescope, a two-color 32 megapixel ccd camera, and a network of computers. On
clear nights the system generates up to 8 GB of raw data and 1 GB of reduced
data. The computer system is responsible for all realtime control tasks, for
data reduction, and for storing all data associated with each observation in a
data base. The subject of this paper is the software system that handles these
functions. It is an integrated system controlled by Petri nets that consists of
multiple processes communicating via mailboxes and a bulletin board. The system
is highly automated, readily extensible, and incorporates flexible error
recovery capabilities. It is implemented with C++ in a Unix environment.
\\


Paper: astro-ph/9611080
From: library@astro.Princeton.EDU
Date: Mon, 11 Nov 1996 11:40:44 -0500 (EST)

Title: Dark Matter
Authors: Neta Bahcall (Princeton University Observatory)
Comments: Figures can be obtained by e-mail to neta@astro.princeton.edu
Report-no: Princeton Observatory Preprint 693
\\
  Observations in the optical, in X-rays, and gravitational lensing of
galaxies, clusters of galaxies, and large-scale structure are beginning to
provide clues to the dark matter problem. I review the impact of these
observations on some of the main questions relating to dark matter: How much
dark matter is there? Where is it located? What is the nature of the dark
matter? and what is the amount of baryonic dark matter.

 (http://xxx.lanl.gov/abs/astro-ph/9611080 ,  9kb)
\\


Paper: astro-ph/9606065
From: Rennan Bar-Kana 

barkana@arcturus.mit.edu
Date: Mon, 10 Jun 1996 16:43:49 -0400

Title: LIMITS ON A STOCHASTIC BACKGROUND OF GRAVITATIONAL WAVES FROM GRAVITATIONAL LENSING
Authors: Rennan Bar-Kana (MIT)
Comments: 12 pages, LaTex + 1 PS Figure, submitted to Phys. Rev. D
\\
  We compute the effects of a stochastic background of gravitational waves on
multiply imaged systems or on weak lensing. There are two possible observable
effects, a static relative deflection of images or shear, and an induced
time-dependent shift or proper motion. We evaluate the rms magnitude of these
effects for a COBE normalized, scale-invariant spectrum, which is an upper
limit on spectra produced by inflation. Previous work has shown that
large-scale structure may cause a relative deflection large enough to affect
observations, but we find that the corresponding effect of gravity waves is
smaller by $\sim 10^4$ and so cannot be observed. This results from the
oscillation in time as well as the redshifting of the amplitude of gravity
waves. We estimate the magnitude of the proper motion induced by deflection of
light due to large-scale structure, and find it to be $\sim 10^{-8}$ arcsec per
year. This corresponds to $\sim 50$ km/s at cosmological distances, which is
quite small compared to typical peculiar velocities. The COBE normalized
gravity wave spectrum produces motions smaller still by $\sim 10^2$. We
conclude that light deflection due to these cosmological perturbations cannot
produce observable proper motions of lensed images. On the other hand, there
are only a few known observational limits on a stochastic background of gravity
waves at astrophysical wavelengths. High-resolution imaging of lens systems
with VLBI can set limits on the relative motions of images. We show that a
limit on gravity waves of $\Omega_{\lambda} \sim 10^{-5}$, valid for
wavelengths $\lambda$ greater than a few pc (up to $\sim 100$ Mpc), is feasible
with a ten-year observation of a four-image system.
(http://xxx.lanl.gov/abs/astro-ph/9606065 ,  20kb)
Paper: astro-ph/9606065
replaced with revised version Mon, 11 Nov 1996 17:30:27 -0500

Title: Limits on a Stochastic Background of Gravitational Waves from
  Gravitational Lensing
Authors: Rennan Bar-Kana (MIT)
Comments: 14 pages, LaTex + 1 PS Figure, accepted version to be published in
  Phys. Rev. D15, Dec. 1996. An incorrect assumption was removed, also various
  other minor changes


 (http://xxx.lanl.gov/abs/astro-ph/9606065 ,  21kb)
\\


Paper: astro-ph/9701068
From: Rennan Bar-Kana barkana@arcturus.mit.edu
Date: Mon, 13 Jan 1997 18:12:25 -0500

Title: Analysis of Time Delays in the Gravitational Lens PG1115+080
Authors: Rennan Bar-Kana (MIT Physics Dept.)
Comments: 14 pages, Latex, submitted to ApJ
\\
  We present a new method for determining time delays among the light curves of
various images in a gravitational lens. The method is based on constructing a
simple model for the source variation and forming a $\chi^2$ measure of the
agreement of this same variation with all of the lightcurves. Our method
provides a simpler and more assumption-free alternative to Press et al. (1992a,
b), but it has similar advantages: it yields an approximate reconstruction of
the source variation and it easily incorporates different assumptions about the
relation between the light curves and about measurement errors. We apply this
method to the light curves of the quadruple gravitational lens PG1115+080
measured by Schechter et al. (1996). Unlike Schechter et al. we include
correlated measurement errors in the analysis, as well as the possibility that
microlensing may cause different images to vary by different factors in flux.
We find a value of $25.0^{+3.3}_{-3.8}$ days (95% confidence) for the delay
between components B and C (close to the 24 day value of Schechter et al.,
and so implying a similar $H_0$ for a given lens model). However, the ratio
$t_{AC}/t_{BA}$ of the two intermediate delays is poorly determined at
$1.13^{+.18}_{-.17}$ (68% confidence), close to the value predicted by lens
models ($\sim 1.4$) unlike the Schechter et al. value ($\sim 0.7$). The
variation ratios of C with respect to A and of A with respect to B are both
different from 1, $1.39^{+.16}_{-.20}$ and $.79^{+.10}_{-.12}$ (95%
confidence), respectively. This is an indication of a microlensing gradient,
and this type of microlensing may allow us to set both an upper and a lower
limit on the size of the quasar optical emission region. (Shortened Abstract)
 (http://xxx.lanl.gov/abs/astro-ph/9701068 ,  49kb)
\\


Paper:astro-ph/9601125
From: A. Bartsch armin@MPA-Garching.MPG.DE
Date: Tue, 23 Jan 1996 20:11:35 +0100 (MET)
Title: REANALYSIS OF THE ASSOCIATION OF HIGH-REDSHIFT 1-JANSKY QUASARS WITH IRAS GALAXIES
Author: Armin Bartsch, Peter Schneider and Matthias Bartelmann
  (Max-Planck-Institut f. Astrophysik)

Comments: 29 pages, LaTex, including 9 figures, submitted to Astronomy and
  Astrophysics
Report-no: MPA 922
\\
  We develop a new statistical method to reanalyse angular correlations between
background QSOs and foreground galaxies that are supposed to be a consequence
of dark matter inhomogeneities acting as weak gravitational lenses. The method
is based on a weighted average over the galaxy positions and is optimized to
distinguish between a random distribution of galaxies around QSOs and a
distribution which follows an assumed QSO-galaxy two-point correlation
function, by choosing an appropriate weight function. With simulations we
demonstrate that this weighted average is slightly more significant than
Spearman's rank-order test which was used in previous investigations. In
particular, the advantages of the weighted average show up if the two-point
correlation function is weak. We then reanalyze the correlation between
high-redshift 1-Jansky QSOs and IRAS galaxies, taken from the IRAS Faint Source
Catalog; these samples were analyzed previously using Spearman's rank-order
test. In agreement with the previous work, we find moderate to strong
correlations between these two samples; considering the angular two-point
correlation function of these samples, we find a typical scale of order $5'$
from which most of the correlation signal derives. However, the statistical
significance of the correlation changes with the redshift slices of the QSO
sample one considers. Comparing with simple theoretical estimates of the
expected correlation, we find that the signal we derive is considerably
stronger than expected. On the other hand, recent direct verifications of the
overdensity of matter in the line-of-sight to high-redshift radio QSOs obtained
from the shear field around these sources, indicates that the observed
association can be attributed to a gravitational lens effect.
(http://xxx.lanl.gov/abs/astro-ph/9601125 ,  73kb)
\\


Paper: astro-ph/9702118
From: richard\_barvainis reb@dopey.haystack.edu
Date: Thu, 13 Feb 1997 10:05:34 EST   (75kb)

Title: Multiple CO Transitions, CI, and HCN from the Cloverleaf Quasar
Authors: Richard Barvainis, Philip Maloney, Robert Antonucci, and Danielle
  Alloin
Comments: 14 pages of text, plus two figures. Requires aaspp4.sty, included. To
  be published in the Astrophysical Journal
\\
  New millimeter-wavelength emission lines are reported for the Cloverleaf
(H1413+117), a gravitationally lensed quasar at redshift 2.56. High
signal-to-noise ratio spectra of four lines in CO (J=3-2, J=4-3, J=5-4, and
J=7-6) have been obtained and are modeled using an escape probability
formalism. The line brightness temperatures are flat or rising between CO(3-2)
and CO(4-3) and then drop to the CO(5-4) and CO(7-6) lines; this falloff
suggests that the optical depths in the CO lines are modest 
$( \tau_{4-3} < 3)$,
and that the gas is relatively warm (T ~ 100 K) and dense $ (n_{H2} > 3 X 10^3
cm^{-3})$. The neutral carbon fine structure line CI(3P1-3P0) was detected with
moderate SNR on two separate occasions, and appears secure. The HCN(4-3) line
is somewhat more tentative, as it was observed only once and detected with
moderate SNR. However, its brightness ratio of 0.25 relative to the CO(4-3)
line is very similar to the ratio seen in luminous infrared galaxies. The
detectability of the Cloverleaf in molecular and neutral atomic transitions is
largely due to high emissivity of the gas and magnification from gravitational
lensing, rather than an extremely large mass of gas.
 ( http://xxx.lanl.gov/abs/astro-ph/9702118 ,  75kb)
\\


Paper: astro-ph/9609183
From: benitezn@astsun2.ifca.unican.es (Narciso Benitez)
Date: Thu, 26 Sep 96 17:09:20 +0200

Title: Large Scale QSO-galaxy correlations for radio loud and optically
  selected QSO samples
Authors: N. Benitez and E. Martinez-Gonzalez, IFCA (CSIC-UC)
Comments: 18 pages, 8 figures, AASTeX, accepted for publication in ApJ
\\
  We have studied the distribution of $B_J<20.5$ galaxies from the ROE/NRL
COSMOS/UKST catalogue around two samples of $z>0.3$ QSOs with similar redshift
distributions. The first sample is formed by 144 radio-loud QSOs from the
Parkes Catalogue, and the other contains 167 optically selected QSOs extracted
from the Large Bright Quasar Survey. It is found that there is a $\approx
99.0\%$ significance level excess of COSMOS/UKST galaxies around the PKS QSOs,
whereas there is a marginal defect of galaxies around the LBQS QSOs. When the
distribution of galaxies around both samples is compared, we found that there
is an overdensity of galaxies around the PKS sample with respect to the LBQS
sample anticorrelated with the distance from the QSOs at a $99.7\%$
significance level. Although this result apparently agrees with the predictions
of the double magnification bias, it is difficult to explain by gravitational
lensing effects alone; dust in the foreground galaxies and selection effects in
the detection of LBQS QSOs should be taken into account. It has been
established that the lines of sight to PKS flat-spectrum QSOs go through
significatively higher foreground galaxy densities than the directions to LBQS
quasars, what may be partially related with the reported reddening of PKS QSOs.
 (http://xxx.lanl.gov/abs/astro-ph/9609183 ,  68kb)
\\


Paper: astro-ph/9703071
From: benitezn@astsun1.ifca.unican.es (Narciso Benitez)
Date: Tue, 11 Mar 97 16:53:17 +0100   (12kb)

Title: Statistical excess of foreground galaxies around high-z radiogalaxies
Authors: N. Benitez, E. Martinez-Gonzalez and J.M. Martin-Mirones (IFCA,
  CSIC-UC)
Comments: 4 pages, 1 figure, A\&A Latex, accepted for publication as a letter to
  A\&A
\\
  K-band imaging of a sample of 21 radiogalaxies with $z \sim 1.5$ reveals the
existence of a statistical association of foreground galaxies with the
positions of the radiosources. The excess is detected within a 1' radius at a
high significance level (>99.8%). K-band light is a good tracer of stellar
mass, so this result indicates the existence of an association between
foreground mass perturbations and background radiosources, as expected from the
magnification bias effect, and confirms previous results obtained for other
high-z radio-loud AGN.
 ( http://xxx.lanl.gov/abs/astro-ph/9703071 ,  12kb)
\\


Paper: astro-ph/9510104
From: bennett@igpp.llnl.gov (Dave Bennett)
Date: Thu, 19 Oct 1995 22:57:24 -0700

Title: THE MACHO PROJECT DARK MATTER SEARCH
Authors: D.P. Bennett, C. Alcock, R.A. Allsman, T.S. Axelrod, K.H. Cook, K.C.
  Freeman, K. Griest, S.L. Marshall, B.A. Peterson, M.R. Pratt, P.J. Quinn,
  A.W. Rodgers, C.W. Stubbs, W. Sutherland (The MACHO Collaboration)
Comments: 12 pages, uuencoded gzip compressed postscript (356 kb). Figures
  included. To appear in the Proceedings of the Astronomical Society of the
  Pacific Symposium on Clusters, Lensing, and the Future of the Universe
\\
  We provide a status report on our search for dark matter in our Galaxy in the
form of massive compact halo objects (or Machos), using gravitational
microlensing of background stars. This search uses a very large format CCD
camera on the dedicated 1.27m telescope at Mt.~Stromlo, Australia, and has been
taking data for almost 3 years. At present, we are in the midst of analyzing
our second year data for 8 million stars in the Large Magellanic Cloud. We find
more microlensing events than expected from known stellar populations
suggesting that Machos are indeed present in the Galactic halo, but the
observed microlensing rate toward the LMC is too small to allow for a halo
dominated by sub-stellar Machos. Our observations of the Galactic bulge have
also yielded substantially more microlensing events than anticipated including
a number of exotic ``deviant" microlensing events. The implications of these
results are discussed. (astro-ph/9510104 ,  256kb)
\\


Paper: astro-ph/9606012
From: bennett@igpp.llnl.gov (Dave Bennett)
Date: Tue, 4 Jun 1996 02:47:28 -0700 (PDT)

Title: A BINARY LENSING EVENT TOWARD THE LMC: OBSERVATIONS AND DARK MATTER IMPLICATIONS
Authors: D.P.Bennett, C.Alcock, R.A.Allsman, D.Alves, T.S.Axelrod, A.Becker,
  K.H.Cook, K.C.Freeman, K.Griest, J.Guern, M.J.Lehner, S.L.Marshall,
  D.Minniti, B.A.Peterson, M.R.Pratt, P.J.Quinn, S.H.Rhie, A.W.Rodgers,
  C.W.Stubbs, W.Sutherland, and D.Welch (The MACHO Collaboration)
Comments: 5 pages, 3 postscript figures included; To appear in the Proceedings
  of the Dark Matter '96 Conference held in Santa Monica, CA, Feb., 1996
\\
  The MACHO collaboration has recently analyzed 2.1 years of photometric data
for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis
has revealed 8 candidate microlensing events and a total microlensing optical
depth of $\tau_{meas} = 2.9 +1.4/-0.9 \times 10^{-7}$. This significantly
exceeds the number of events (1.1) and the microlensing optical depth predicted
from known stellar populations: $\tau_{back} = 5.4\times 10^{-8}$, but it is
consistent with models in which about half of the standard dark halo mass is
composed of Machos of mass $\simeq 0.5 M_\odot$. One of these 8 events appears to
be a binary lensing event with a caustic crossing that is partially resolved
which allows us to estimate the distance to the lenses. If the source star is
not a short period binary star, then we show that the lens system is very
likely to reside in the LMC. However, if we assume that the optical depth for
LMC-LMC lensing is large enough to account for our entire lensing signal, then
the binary event does not appear to be consistent with lensing of a single LMC
source star by a binary residing in the LMC. Thus, while the binary lens may
indeed reside in the LMC, there is no indication that most of the lenses reside
in the LMC.
(http://xxx.lanl.gov/abs/astro-ph/9606012 ,  77kb)
\\


Paper: astro-ph/9612208
From: David Bennett bennett@bustard.phys.nd.edu
Date: Sat, 21 Dec 1996 10:57:10 -0500

Title: Planetary Microlensing from the MACHO Project
Authors: The MACHO Collaboration: D.P.Bennett, C.Alcock, R.A.Allsman, D.Alves,
  T.S.Axelrod, A.Becker, K.H.Cook, K.C.Freeman, K.Griest, M.J.Lehner,
  S.L.Marshall, D.Minniti, B.A.Peterson, M.R.Pratt, P.J.Quinn, S.H.Rhie,
  A.W.Rodgers, C.W.Stubbs, W.Sutherland, T.Vandehei and D.Welch
Comments: 5 pages, Latex, 5 postscript figures included, To appear in the
  Proceedings of "Planets Beyond the Solar System and the Next Generation of
  Space Missions", held at STScI, October 16-18, 1996
\\
  We present the lightcurves of two microlensing events from the MACHO Project
data that are likely to be due to lenses with masses similar to Jupiter's mass.
Although the MACHO Project survey data are not sufficient to definitively
establish the identification of planetary mass lenses in these cases,
observations by microlensing follow-up networks such as GMAN and PLANET should
be able to definitively determine the planetary nature of similar events which
may occur in the near future.
 (http://xxx.lanl.gov/abs/astro-ph/9612208 ,  88kb)
\\


Paper: astro-ph/9610060
From: "Giulio Mignola, ++ 41 22 767 3572" <MIGNOLA@vxcern.cern.ch>
Date: Wed, 9 Oct 1996 17:51:33 +0200 (CET-DST)

Title: On neutralino stars as microlensing objects
Author: V. Berezinsky, A. Bottino and G. Mignola
Comments: 7 pages, LaTeX, no figures
Report-no: CERN-TH 96-283, DFTT 53/96
\\
  The microlensing objects, Machos, recently observed in the halo of our
Galaxy, can be interpreted as dense neutralino objects, neutralino stars,
produced by the gravitational instability of neutralino gas. Taking the mass
and radius of these objects from microlensing observations we calculated the
diffuse gamma-ray flux produced in neutralino--neutralino annihilation inside
the objects. The resulting flux is many orders of magnitude higher than the
observed one.
 (http://xxx.lanl.gov/abs/astro-ph/9610060 ,  8kb)
\\

Paper: astro-ph/9611012
From: fbernard@wasa.saclay.cea.fr (Francis Bernardeau)
Date: Sat, 2 Nov 1996 12:14:04 +0100

Title: Weak Lensing Detection in CMB Maps
Authors: F. Bernardeau (SPhT Saclay)
Comments: 13 pages; Submitted to Astronomy and Astrophysics
Report-no: Saclay SPhT T96/122
\\
 The weak lensing effects are known to change only weakly the shape of the
power spectrum of the Cosmic Microwave Background (CMB) temperature
fluctuations. I show here that they nonetheless induce specific non-Gaussian
effects that can be detectable with the four-point correlation function of the
CMB anisotropies. The magnitude and geometrical dependences of this correlation
function are investigated in detail. It is thus found to scale as the square of
the derivative of the two-point correlation function and as the angular
correlation function of the gravitational displacement field. It also contains
specific dependences on the shape of the quadrangle formed by the four
directions.
  When averaged at a given scale, the four-point function, that identifies with
the connected part of the fourth moment of the probability distribution
function of the local filtered temperature, scales as the square of logarithmic
slope of its second moment, and as the variance of the gravitational
magnification at the same angular scale.
  All these effects have been computed for specific cosmological models. I
stress that, as the amplitude of the gravitational lens effects has a specific
dependence on the cosmological parameters, the detection of the four-point
correlation function can provide precious complementary constraints to those
brought by the temperature power spectrum.
 (http://xxx.lanl.gov/abs/astro-ph/9611012 ,  73kb)

Paper: astro-ph/9611012
replaced with revised version Wed, 5 Mar 1997 16:55:13 +0100

Title: Weak Lensing Detection in CMB Maps
Authors: F. Bernardeau (SPhT Saclay)
Comments: 13 pages; revised version, in press in Astronomy and Astrophysics
Report-no: Saclay SPhT T96/122
 ( http://xxx.lanl.gov/abs/astro-ph/9611012 ,  73kb)
\\


Paper: astro-ph/9702140
From: Orfeu Bertolami orfeu@cosmos.ist.utl.pt
Date: Mon, 17 Feb 1997 13:06:27 GMT   (6kb)

Title: Weak Lensing, Shear and the Cosmic Virial Theorem in a Model with a
  Scale-Dependent Gravitational Coupling
Authors: Orfeu Bertolami
Comments: Latex file. To be published in Gen. Relativity and Gravitation
Report-no: DF/IST-1.96
\\
  It is argued that, in models where the gravitational coupling is
scale-dependent, predictions concerning weak gravitational lensing and shear
are essentially similar to the ones derived from General Relativity. This is
consistent with recent negative results of observations of the MS1224, CL2218
and A1689 systems aimimg to infer from those methods the presence of dark
matter. It is shown, however, that the situation is quite different in what
concerns an analysis based on the Cosmic Virial Theorem.
 ( http://xxx.lanl.gov/abs/astro-ph/9702140 ,  6kb)
\\


Paper: astro-ph/9606064
From: bezecour@srvdec.obs-mip.fr (jocelyn bezecourt)
Date: Mon, 10 Jun 1996 22:03:26 +0200

Title: REDSHIFT SURVEY OF GRAVITATIONAL ARCLETS IN ABELL 2390
Authors: J. Bezecourt and G. Soucail (Observatoire Midi-Pyrenees, Toulouse)
Comments: 10 pages, Latex with 10 postscript figures, accepted by Astronomy and
  Astrophysics, postscript file also available by anonymous ftp at
  ftp://summer.obs-mip.fr/pub/OUTGOING/a2390.ps. or upon request at
  bezecour@obs-mip.fr
\\
  In this paper, we present new determinations of redshifts on a sample of
gravitational arclets identified in the cluster of galaxies Abell 2390. The
arclets candidates were selected from their elongated morphology as seen in
recent deep HST images of the cluster. The spectra display various features,
and the redshifts of the background objects range from 0.398 to 1.268, most of
them being between 0.6 and 0.9 with [O II] $\lambda$=3727\AA\ being the main
emission line encountered. This distribution is mostly concentrated in two
redshifts planes at $z=0.64$ and $z=0.90$. The existence of two pairs of
background galaxies at different redshifts, almost superimposed on the same
line of sight are used to infer some limits on the mass of galaxy-size
deflectors. A detailed writing of the lensing distorsion by two lens planes at
different redshifts is developped for this purpose. Finally, [O II] equivalent
widths are used to compute approximate star formation rates which appear to be
of the same order of magnitude as in nearby spiral galaxies. The implications
on both the lensing properties of the cluster and the analysis of the field
galaxy evolution are also discussed.
(http://xxx.lanl.gov/abs/astro-ph/9606064 ,  245kb)
\\


Paper: astro-ph/9612026
From: Ortwin Gerhard gerhard@astro.unibas.ch
Date: Tue, 3 Dec 1996 09:42:31 +0100 (MET)

Title: Microlensing Optical Depth of the COBE Bulge
Authors: N. Bissantz (1,2), P. Englmaier (1), J. Binney (3), O. Gerhard (1)
  ((1) Astron.Inst., Univ.Basel, CH, (2) Phys.Inst., Univ.Freiburg, D, (3)
  Dpt. Theoret. Phys., Oxford, UK)
Comments: 9 pages, TeX. 7 figures (gif). Submitted to MNRAS. Also available
  with full resolution figures as ps-file at
  http://www.astro.unibas.ch/dynamics/papers.html
Report-no: Basel Preprint No.97
\\
  We examine the left-right asymmetry in the cleaned COBE/DIRBE near-infrared
data of the inner Galaxy and show (i) that the Galactic bar is probably not
seen very nearly end-on, and (ii) that even if it is, it is not highly
elongated. The assumption of constant mass-to-light ratio is used to derive
simulated terminal-velocity plots for the ISM from our model luminosity
distributions. By comparing these plots with observed terminal velocities we
determine the mass-to-light ratio of the near-IR bulge and disk.
   Assuming that all this mass contributes to gravitational microlensing we
compute optical depths $\tau$ for microlensing in Galactic-centre fields. For
three models with bar major axis between $10\deg-25\deg$ from the Sun-Galactic
Center line, the resulting optical depths in Baade's window lie in the range
$0.83\times10^{-6} < \tau < 0.89\times10^{-6}$ for main-sequence stars
and $1.2\times10^{-6} < \tau < 1.3\times10^{-6}$ for red-clump giants. We
discuss a number of uncertainties including possible variations of the
near-infrared mass-to-light ratio. We conclude that, although the values
predicted from analyzing the COBE and gas velocity data are inconsistent at the
$2-2.5\sigma$ level with recent observational determinations of $\tau$, we
believe they should be taken seriously.
 (http://xxx.lanl.gov/abs/astro-ph/9612026 ,  108kb)
\\


Paper: astro-ph/9608154
From: borra@phy.ulaval.ca (Ermanno Borra)
Date: Fri, 23 Aug 1996 19:16:44 -0400

Title: Liquid Mirror Telescopes: A progress report
Authors: Ermanno F. Borra, Marc Ferrari, Luc Girard, Gilberto Moretto, Gregoire
  Tremblay and Gerard Lemaitre
Comments: To appear in the SPIE conference proceedings 'Optical Telescopes of
  Today and Tomorrow', May 29 - June1, Landskrona/Hven, Sweden, Additional info
  on LMs at: http://astrosun.phy.ulaval.ca/lmt/lmt-home.html
\\
  We review the present status of liquid mirror telescopes. Interferometric
tests of liquid mirrors (the largest one having a diameter of 2.5 meters ) show
excellent optical qualities. The basic technology is now sufficiently reliable
that it can be put to work. Indeed, a handful of liquid mirrors have now been
built that are used for scientific work. A 3.7-m diameter LMT is presently
being built in the new Laval upgraded testing facilities. Construction of the
mirror can be followed on the Web site: http://astrosun.phy.ulaval.ca/lmt/lmt-
home.html. Finally we address the issue of the field accessible to LMTs
equipped with novel optical correctors. Optical design work, and some
exploratory laboratory work, indicate that a single LMT should be able to
access, with excellent images, small regions anywhere inside fields as large as
45 degrees.
 (http://xxx.lanl.gov/abs/astro-ph/9608154 ,  308kb)
\\


Paper: astro-ph/9612151
From: Ian Smail <ian.smail@durham.ac.uk>
Date: Mon, 16 Dec 1996 07:15:55 MST

Title: A Weak Lensing Survey in the Fields of z~1 Luminous Radio Sources
Authors: Richard G. Bower and Ian Smail
Comments: 10 pages, Latex, 3 figures, uses mn.sty and psfig.sty. Submitted to
  MNRAS
\\
  In this paper we present weak lensing observations of the fields around 8 z~1
luminous radio sources. These data are searched for the lensing signatures of
clusters that are either physically associated with the radio objects, or are
foreground systems projected along the line of sight. The radio sources were
all imaged with WFPC-2/HST providing high quality shape information on large
numbers of faint galaxies around them. Statistical analysis of the coherent
shear field visible in the shapes of the faint galaxies indicates that we have
detected a weak lensing signal close to one of the targets, 3C336 at z=0.927,
with a high level of confidence. A second, independent WFPC-2 observation of
this target reinforces this detection. Our results support the earlier
suggestion of weak lensing in this field by Fort et al (1996) using
ground-based data. We also combined the shear distributions in the remaining 7
field to improve our sensitivity to weak shear signals from any structure
typically associated with these sources. We find no detectable signal and
estimate an upper limit on the maximum shear allowed by our observations. Using
an N(z) estimated from lensing analyses we convert our observed lensing signal
and limits into estimates of the masses of the various structures. We suggest
that further lensing observations of distant radio sources and their host
environments may allow the cluster $L_X$-mass relationship to be mapped at
high-z. This is crucial for interpreting the results of the next generation of
deep X-ray surveys, and thus constraining the redshift evolution of the cluster
mass function out to z=1.
 (http://xxx.lanl.gov/abs/astro-ph/9612151 ,  197kb)
\\


Paper: astro-ph/9511150
From: tjb@wibble.berkeley.edu (tom broadhurst)
Date: Thu, 30 Nov 1995 20:31:02 -0800
Date (revised): Thu, 30 Nov 1995 21:04:52 -0800

Title:GRAVITATIONAL `CONVERGENCE' AND CLUSTER MASSES
Authors: Tom Broadhurst
Comments: 12 pages, compressed uuencoded, 3 figures
Journal-ref: apjl, submitted
\\
  Two colour photometry of the cluster A1689 reveals a `relative
magnification-bias' between lensed blue and red background galaxies, arising
from a dependence of the faint galaxy count-slope on colour. The colour
distribution is skewed blueward of the far field, allowing us to measure the
cluster magnification and to understand the notorious blueness of large arcs.
We show that the magnification information can be combined with the usual image
distortion measurements to isolate the local `convergence' component of lensing
and hence derive the projected mass. This is achieved through a simple local
relation between the convergence and the observables, which can be applied
generally over the surface a cluster. In the weak lensing limit, the
convergence reduces to a dependence on the magnification alone, so that in the
outskirts of clusters the surface-density of matter is obtained directly from
the surface-density of background galaxies. Hence, useful lensing work requires
colour information but not necessarily good seeing. Interestingly, convergence
varies slowly at high redshift, saturating at a level depending on the Horizon
distance, allowing a useful model-independent measurement of the Global
Geometry.
(astro-ph/9511150 ,  86kb)
\\


Paper: astro-ph/9604144
From: ari@parsifal.phys.columbia.edu (Ari Buchalter)
Date: Wed, 24 Apr 96 18:37:16 EDT

Title: RATES FOR PARALAX-SHIFTED MICROLENSING EVENTS FROM GROUND-BASED OBSERVATIONS OF THE GALACTIC BULGE
Authors: Ari Buchalter (Columbia University) and Marc Kamionkowski (Columbia
  University)
Comments: 25 pages, 7 Postscript figures
Report-no: CAL-603, CU-TP-744
\\
  The parallax effect in ground-based microlensing (ML) observations consists
of a distortion to the standard ML light curve arising from the Earth's orbital
motion. In most cases, the resolution in current ML surveys is not accurate
enough to observe this effect, but parallax could conceivably be detected with
frequent followup observations of ML events in progress. We calculate the
expected fraction of events where parallax distortions will be detected by such
observations, adopting Galactic models consistent with the observed ML
timescale ($t_0$) distributions. We study the dependence of the rates for
parallax-shifted events on the sampling frequency and on the photometric
precision. For example, we find that for hourly observations with typical
photometric errors of 0.01 mag, 6\% of events where the lens is in the bulge,
and 31\% of events where the lens is in the disk, (or $\simeq 10$\% of events
overall) will give rise to a measurable parallax shift at the 95\% confidence
level. These fractions may be increased by improved photometric accuracy and
increased sampling frequency. Parallax measurements yield the reduced
transverse speed, $\tilde{v}$, which gives both the relative transverse speed
and lens mass as functions of distance. We give examples of the accuracies with
which $\tilde{v}$ may be measured in typical parallax events. Using only the 3
standard ML parameters to fit ML light curves which may be shape-distorted by
parallax or blending, can result in incorrect inferred values for these
quantities. We find that the inferred timescales from such fits tend to shift
the event duration distribution by $\simeq 10$\% towards shorter $t_0$ for
events with disk lenses, but do not affect bulge lenses. In both cases, the
impact-parameter distribution is depressed slightly at the low and high ends.
(http://xxx.lanl.gov/abs/astro-ph/9604144 ,  102kb)
\\


Paper:astro-ph/9601031
From:P.Schneider peter@MPA-Garching.MPG.DE
Date: Tue, 9 Jan 1996 11:26:06 +0100 (MET)

Title: VERY CLOSE PAIRS OF QUASI-STELLAR OBJECTS
Authors: G. Burbidge, F. Hoyle and P. Schneider
Comments: 8 pages, including 1 figure, submitted to Astronomy and Astrophysics
  Letters
Report-no: MPA 916
\\
  It is pointed out that there are now known four very close pairs of QSOs with
separations < 5 arcsec and very different redshifts. Several estimates of the
probability that they are accidental configurations range between $10^{-7}$ and
3.5 x $10^{-3}$. We conclude either that this is further evidence that QSOs have significant non-cosmological redshift components, or that thave significant
non-cosmological redshift components, or that the pairs must be explained by
gravitational lensing. (astro-ph/9601031 ,  17kb)
\\


Paper: astro-ph/9610074
From: CAPOZZIELLO@astrna.na.astro.it
Date: Thu, 10 Oct 1996 18:18:48 +0100 (CET)

Title: Luminosity variation in (de)focusing microlensing
Authors: Salvatore Capozziello, Ruggiero de Ritis, Vladimir Mank'o, Alma Angela
  Marino, Giuseppe Marmo
Comments: 9 pages, latex, submitted to Phys. Lett. A
\\
  The luminosity variation of a stellar source due to the gravitational
microlensing effect can be considered also if the light rays are defocused
(instead of focused) toward the observer. In this case, we should detect a gap
instead of a peak in the light curve of the source. Actually, we describe how
the phenomenon depends on the relative position of source and lens with respect
to the observer: if the lens is between, we have focusing, if the lens is
behind, we have defocusing. It is shown that the number of events with
predicted gaps is equal to the number of events with peaks in the light curves.
 (http://xxx.lanl.gov/abs/astro-ph/9610074 ,  11kb)
\\


Paper: astro-ph/9610161
From: CAPOZZIELLO@napoli.infn.it
Date: Mon, 21 Oct 1996 19:39:46 +0100 (CET)

Title: Defocusing gravitational microlensing
Authors: Salvatore Capozziello, Ruggiero de Ritis, Vladimir Mank'o, Alma Angela
  Marino, Giuseppe Marmo
Comments: 19 pages, latex, submitted to Physica Scripta
\\
  We introduce the notion of defocusing gravitational lens considering a MACHO
located behind a light source with respect to an observer. The consequence of
defocusing effect is a temporal variability of star luminosity which produces a
gap instead of a peak as tell--tale signature in the light curve. General
theory of (de)focusing rays (geodesics) in a gravitational field is presented.
Furthermore, we give estimations of the mass of the lens and the optical depth
connected to such a phenomenon.
 (http://xxx.lanl.gov/abs/astro-ph/9610161 ,  18kb)
\\


Paper: astro-ph/9610232
From: Fabio Governato 

fabio@hermes.astro.washington.edu
Date: Mon, 28 Oct 1996 19:07:52 MST

Title: Prospects for Cosmology with Cluster Mass Profiles
Authors: Mary Crone, Fabio Governato, Joachim Stadel and Thomas Quinn
Comments: 11 pages, 2 postscript figures included. Submitted to ApJL. .ps
  version also available at
  http://www-hpcc.astro.washington.edu/faculty/fabio/index.html
\\
  We test the precision with which weak lensing data can provide characteristic
cluster mass profiles within Cold Dark Matter scenarios. Using a parallel
treecode to simulate volumes as large as 500h-1 Mpc with good resolution, we
generate samples of large clusters within a standard CDM model and an open CDM
model with $Omega_0=0.3$. We mock high-quality lensing data by including
realistic errors, selecting cluster samples based on velocity dispersion, and
fitting profiles within a realistic range in radius. We find that a sample of
ten clusters can determine logarithmic profile slopes with 1 sigma errors of
about 7%. Increasing the sample size to twenty brings this error down to less
than 5%, but this is still insufficient to distinguish the two models. However,
measures of cluster profiles obtained with weak lensing do place strong
constraints for general CDM--like models of structure formation, and we discuss
the optimal strategy for obtaining data samples to use for this purpose.
 (http://xxx.lanl.gov/abs/astro-ph/9610232 ,  26kb)
\\


Paper: astro-ph/9610067
From: arlin@astro.columbia.edu (Arlin Crotts)
Date: Wed, 9 Oct 1996 21:01:09 -0400

Title: VATT/Columbia Microlensing Survey of M31 and the Galaxy
Authors: Arlin P.S. Crotts (Columbia U.)
Comments: presented at the International Conference on "Dark and Visible Matter
  in Galaxies" (Sesto Pusteria, Italy, 2-5 July 1996), 8 pages, Latex, 3
  required .sty files (incl. paspconf.sty), 4 figs.
\\
  We describe the results and outline the methods used in a search for
microlensing events affecting stars in the outer bulge and inner disk of M31,
due both to masses in M31 and the Galaxy. These observations, from 1994 and
1995 on the Vatican Advanced Technology Telescope and KPNO 4m, rule out masses
over much of the range from ~10e-7 Msol to 0.08 Msol as the primary
constituents of the mass of M31 and the Galaxy towards this field. Furthermore
we find six candidate events consistent with microlensing due to masses of
about 1 Msol, but we suspect that some of these may be cases where long-period
red supergiant variables may be mistaken for microlensing events. Coverage from
anticipated data should be helpful in determining if these sources maintain a
constant baseline, and therefore are best described by microlensing events. We
analyzed our data using the new technique of "difference image photometry"
(also called "pixel lensing"). A brief overview of this technique is included
in the Appendix I. This contribution summarizes two other recent papers
(Tomaney and Crotts 1996, Crotts and Tomaney 1996).
 (http://xxx.lanl.gov/abs/astro-ph/9610067 ,  128kb)
\\


Paper: astro-ph/9702033
From: delaix@theory6.phys.cwru.edu (Andrew de Laix)
Date: Mon, 3 Feb 1997 15:04:40 -0500   (44kb)

Title: Gravitational Lensing Signature of Long Cosmic Strings
Authors: Andrew A. de Laix, Lawrence M. Krauss, and Tanmay Vachaspati
Comments: 4 pages, revtex with 3 postscript figures included
Report-no: CWRU-P1-97
\\
  The gravitational lensing by long, wiggly cosmic strings is shown to produce
a large number of lensed images of a background source. In addition to pairs of
images on either side of the string, a number of small images outline the
string due to small-scale structure on the string. This image pattern could
provide a highly distinctive signature of cosmic strings. Since the optical
depth for multiple imaging of distant quasar sources by long strings may be
comparable to that by galaxies, these image patterns should be clearly
observable in the next generation of redshift surveys such as the Sloan Digital
Sky Survey.
 ( http://xxx.lanl.gov/abs/astro-ph/9702033 ,  44kb)
\\


Paper: astro-ph/9605171
From: delaix@theory6.phys.cwru.edu (Andrew de Laix)
Date: Tue, 28 May 1996 13:11:10 -0400

Title: GRAVITATIONAL LENSING BY COSMIC STRING LOOPS
Authors: Andrew A de Laix and Tanmay Vachaspati
Comments: 17 pages, RevTex with 1 pict and 9 postscript figures. Postscript
  figures are 100dpi bitmaps ( full resuolution figures are available at
  http://cwsing.phys.cwru.edu/preprints )
Report-no: CWRU-P9-1996
\\
  We calculate the deflection of a light ray caused by the gravitational field
of a cosmic string loop in the weak field limit and reduce the problem to a
single quadrature over a time slice of the loop's world sheet. We then apply
this formalism to the problem of gravitational lensing by cosmic string loops.
In particular, we find an analytic solution for the special case of a circular
loop perpendicular to the optical axis. As examples of more complicated loops,
we consider two loops with higher frequency Fourier modes. The numerical
analysis illustrates the general features of loop lenses. Our estimates, using
typical parameters for GUT scale loops, show that the stringy nature of loop
lenses can be observed for lensing systems involving high redshift galaxies ($z
\sim 2$), and we suggest that gravitational lensing can confirm the existence
of GUT scale strings if they are the seeds for large scale structure formation.
(http://xxx.lanl.gov/abs/astro-ph/9605171 ,  117kb)
\\


Paper: astro-ph/9702088
From: rd@cfata5.harvard.edu (Rosanne Di Stefano)
Date: Mon, 10 Feb 1997 19:04:31 -0500   (393kb)

Title: Identifying Microlensing by Binaries
Authors: Rosanne Di Stefano, Rosalba Perna
Comments: 22 pages, 5 figures; submitted to ApJL 11 December 96; resubmitted to
  ApJ 7 February 1997
\\
  The microlensing monitoring programs have studied large numbers of standard
light curves which seem to be due to lensing by a dark point mass. Theory
predicts that many microlensing events should display significant deviations
from the standard form. Lens binarity in particular is expected to be common.
So far, however, only a handful of light curves exhibit evidence that the lens
is a binary; all of these display dramatic deviations from the standard light
curve, exhibiting pronounced multiple peaks and/or caustic crossings.
Binary-lens events in which the light curve is less dramatically perturbed
should also exist in the data set. Why, then, have we not detected them? The
answer may lie in the fact that the perturbations, though often significant,
tend to be less distinctive than those associated with caustic crossings.
  We present a method to determine whether a light curve is due to lensing by a
binary. The method works for both gently and dramatically perturbed binary-lens
light curves. Our method identifies all degenerate solutions-- i.e., all
possible lensing events that might have given rise to the observed light curve.
It also enables us to eliminate from consideration large ranges of possible
false positive identifications associated with light curves that might mimic
microlensing by a binary. This method, or a generalization of it, can also be
applied to the analysis of light curves that deviate from the standard
point-mass lens form because of astronomical effects other than lens binarity.
 ( http://xxx.lanl.gov/abs/astro-ph/9702088 ,  392kb)
\\


Paper: astro-ph/9701035
From: Martin Dominik dominik@hal1.physik.uni-dortmund.de
Date: Wed, 8 Jan 1997 09:54:47 MST

Title: Estimating physical quantities for an observed galactic microlensing
  event
Authors: M. Dominik
Comments: 23 pages in LaTex2e format including 6 PostScript figures
Reort-no: DO-TH 96/28
\\
  For a given spatial distribution of the lenses and distribution of the
transverse velocity of the lens relative to the line-of-sight, a probability
distribution for the lens mass for a single observed event is derived. In
addition, similar probability distributions are derived for the Einstein radius
and the separation of the lens objects and their rotation period for a binary
lens. These probability distributions are distinct from the distributions for
the lens population, as investigated e.g. by the mass moment method of De
Rujula, Jetzer, and Masso (1991). However, it is shown that the expectation
value for the mass from the probability distribution coincides with the value
from the mass moment method applied to a single observed event. The special
cases of a Maxwellian velocity distribution and of a constant velocity are
discussed in detail. For a rudimentary model of the Galactic halo, the
probability distributions are shown and the relations between the expectation
values of the physical quantities and the event timescale are given. For this
model, it is shown that within a 95.4%-interval around the expectation value,
the mass varies by a factor of 800.
 (http://xxx.lanl.gov/abs/astro-ph/9701035 ,  88kb)
\\


Paper: astro-ph/9702039
From: Martin Dominik dominik@hal1.physik.uni-dortmund.de
Date: Tue, 4 Feb 1997 07:35:37 MST   (165kb)

Title: Galactic microlensing with rotating binaries
Authors: M. Dominik
Comments: 34 pages LaTeX2e format including 18 PostScript figures
Report-no: DO-TH 97/05
\\
  The influence of rotating binary systems on the light curves of galactic
microlensing events is studied. Three different rotating binary systems are
discussed: a rotating binary lens, a rotating binary source, and the motion of
the earth around the sun (parallax effect). The most dramatic effects arise
from the motion of a binary lens because of the changes of the caustic
structure with time. I discuss when the treatment of a microlensing event with
a static binary model is appropriate. It is shown that additional constraints
on the unknown physical quantities of the lens system arise from a fit with a
rotating binary lens as well as from the earth-around-sun motion. For the 
DUO No2
event, a fit with a rotating binary lens is presented.
 ( http://xxx.lanl.gov/abs/astro-ph/9702039 ,  165kb)
\\


Paper: astro-ph/9703003
From: Martin Dominik <dominik@hal1.physik.uni-dortmund.de>
Date: Fri, 28 Feb 1997 06:25:44 MST   (450kb)

Title: Ambiguities in fits of binary lens galactic microlensing events
Authors: M. Dominik
Comments: 35 pages in LaTeX2e format including 37 PostScript figures
Report-no: DO-TH 97/06
\\
  For observed galactic microlensing events only one fit is usually presented,
though, especially for a binary lens, several fits may be possible. This has
been shown for the MACHO LMC No1 event (Dominik \& Hirshfeld 1996). Here I discuss
the strong binary lens events OGLE No7 and DUO No2. It is shown that several models
with a large variety of parameters are possible. For most of the fits,
1-sigma-bounds on the fit parameters are given. The variation of the parameters
within the bounds is in some cases considerable.
 ( http://xxx.lanl.gov/abs/astro-ph/9703003 ,  450kb)
\\


Paper: astro-ph/9611004
From: Ian Smail ian.smail@durham.ac.uk
Date: Fri, 1 Nov 1996 10:11:24 MST

Title: HST Observations of Distant Clusters: Implications for Galaxy Evolution
Authors: Alan Dressler and Ian Smail
Comments: 9 pages, Latex, 3 figures, hx37\_latex.sty included. Invited review to
  appear in the proceedings of the 37th Herstmonceux conference ``HST and the
  High Redshift Universe''
\\
  The ``MORPHS'' group has completed the cataloging, parameterization, and
morphological classification of ~2000 galaxies in 10 rich clusters from 0.36 <
z < 0.56. From a weak lensing analysis using these data, which compares the
X-ray properties ($L_X$) of the clusters with virial temperature estimates 
$(T_v)$ 
from the lensing shear strength, we find little evidence for evolution in the
$L_X-T_v$ relation from that observed for local clusters. We discuss how this
observation constrains models for the X-ray evolution of clusters. The data
have also been used to study the color dispersion of bona-fide ellipticals in
high-z clusters: we find the spread to be very small, suggesting an early
formation epoch for the stellar populations of cluster ellipticals. This is
consistent with the evolution of the morphology-density relationship, in which
we find ellipticals to be as abundant at z=0.5 as in clusters today, and
already well ensconced in the dense regions. In contrast, S0's are less
plentiful and less well-concentrated compared to the present epoch, and spiral
galaxies everywhere more abundant. Combined with other spectroscopic and
morphological data, these observations suggest that most of these rapidly
evolving systems are not likely to become bright ellipticals, which were more
likely formed at early epochs. Cluster S0 galaxies, on the other hand, are
likely to have been produced in large numbers in the recent past.
 (http://xxx.lanl.gov/abs/astro-ph/9611004 ,  27kb)
\\ 


Paper: astro-ph/9703169
From: Timothy Ebbels tebbels@ast.cam.ac.uk
Date: Wed, 26 Mar 1997 05:31:48 MST   (214kb)

Title: Spectroscopic Confirmation of Redshifts Predicted by Gravitational
  Lensing
Authors: Tim Ebbels, Richard Ellis, Jean-Paul Kneib, Jean-Francois Le Borgne,
  Roser Pello, Ian Smail and Blai Sanahuja
Comments: 20 pages, LaTeX, 18 figures. Submitted to MNRAS. Figures 1,8,9,10 \&
  11 and whole paper available at ftp://ftp.ast.cam.ac.uk/pub/tebbels/a2218inv/
\\
  We present deep spectroscopic measurements of 18 distant field galaxies
identified as gravitationally-lensed arcs in a Hubble Space Telescope image of
the cluster Abell 2218. Redshifts of these objects were predicted by Kneib et
al. (1996) using a lensing analysis constrained by the properties of two bright
arcs of known redshift and other multiply-imaged sources. The new spectroscopic
identifications were obtained using long exposures with the LDSS-2 spectrograph
on the William Herschel Telescope and demonstrate the capability of that
instrument to new limits, $R\simeq$24; the lensing magnification implies true
source magnitudes as faint as $R\simeq$25. Statistically, our measured
redshifts are in excellent agreement with those predicted from Kneib et al.'s
lensing analysis which gives considerable support to the redshift distribution
derived by the lensing inversion method for the more numerous and fainter
arclets extending to $R\simeq 25.5$. We explore the remaining uncertainties
arising from both the mass distribution in the central regions of Abell 2218
and the inversion method itself, and conclude that the mean redshift of the
faint field population at $R\simeq$25.5 ($B\sim 26$-27) is low, $<z>$=0.8-1. We
discuss this result in the context of redshift distributions estimated from
multi-colour photometry. Although such comparisons are not straightforward, we
suggest that photometric techniques may achieve a reasonable level of agreement
particularly when they include near-infrared photometry with discriminatory
capabilities in the $1<z<$2 range.
 ( http://xxx.lanl.gov/abs/astro-ph/9703169 ,  214kb)
\\


Paper: astro-ph/9702152
From: Emilio E. Falco falco@aperea.harvard.edu
Date: Tue, 18 Feb 1997 09:16:17 MST   (283kb)

Title: An estimate of $H_0$ from Keck spectroscopy of the gravitational lens
  system 0957+561
Authors: Emilio E. Falco, Irwin I. Shapiro (CfA), Leonidas A. Moustakas, Marc
  Davis (Berkeley)
Comments: 29 pages, 12 .eps figs, AAS Latex, ApJ, in press
\\
  We present long-slit LRIS/Keck spectroscopic observations of the
gravitational lens system 0957+561. Averaged over all of our data, the
rest-frame velocity dispersion $sigma_v$ of the central lens galaxy G1 is $sigma_v$
= 279 +- 12 km/s. However, there appears to be a significant decrease in
$sigma_v$ as a function of distance from the center of G1 that is not typical of
brightest cluster galaxies. Within 0.2" of the center of G1, we find the
average $sigma_v$ = 316+- 14 km/s, whereas for positions > 0.2" from the center
of G1, we find the average $sigma_v$= 266+-12 km/s. A plausible explanation is
that G1 contains a central massive dark object of mass $M_MDO ~ 4x10^9$
$h_100^{-1}$ $M_sun$ ($h_100$ = $H_0$/100km/s/Mpc), which contributes to the central
velocity dispersion, and that the outer value of $sigma_v$ is the appropriate
measure of the depth of the potential well of G1. The determination of a
luminosity-weighted estimate of $sigma_v$ is essential for a determination of 
$H_0$ 
from 0957+561; our accurate measurements remove one of the chief uncertainties
in the assumed form of the mass distribution of the lens. Thus, with the recent
apparent reduction in the uncertainty in the measurement of the time delay for
the images A and B of 0957+561, $\Delta \tau_BA = 417+-3 d$ (Kundic et al. 
1996),
we obtain an estimate for the Hubble constant: $H_0 = 62+-7 km/s/Mpc$. If for
some reason the trend of $sigma_v$ with slit position is spurious and we should
use the dispersion averaged along the slit, then the estimate of $H_0$ 
increases
to 67+-8 km/s/Mpc. These standard errors do not, however, include any
contribution from any errors in the assumed form of the mass distribution of
the lens. In particular, we used the mass model described by Falco, Gorenstein
\& Shapiro (1991), as updated by Grogin \& Narayan (1996a, b). The reduced 
$\chi^2$
 ( http://xxx.lanl.gov/abs/astro-ph/9702152 ,  161kb)
\\


Paper: astro-ph/9610164
From: FARAONI@phastf.phys.UVic.CA
Date: Mon, 21 Oct 1996 14:02:09 -0700 (PDT)

Title: The creation of multiple images by a gravitational wave
Author: Valerio Faraoni (University of Victoria)
Comments: latex, 7 pages, no figures, to appear in Proceedings of the Pacific
  Conference on Gravitation and Cosmology, Seoul, Korea 1996
\\
  We describe gravitational lensing by a gravitational wave, in the regime in
which multiple images of a light source are created. We adapt the vector
formalism employed for ordinary gravitational lenses to the case of a
non-stationary spacetime, and we derive an approximate condition for multiple
imaging. It is shown that certain astrophysical sources of gravitational waves
satisfy this condition.
 (http://xxx.lanl.gov/abs/astro-ph/9610164 ,  6kb)
\\


Paper: astro-ph/9703189
From: "Phil Fischer" philf@astro.lsa.umich.edu
Date: Thu, 27 Mar 1997 23:34:46 -0500   (114kb)

Title: The Mass distribution of the Most Luminous X-ray Cluster RXJ1347.5-1145
  from Gravitational Lensing
Authors: Philippe Fischer, J. Anthony Tyson
Comments: 21 Pages LaTeX, AASTEX version 4 macros, Accepted for publication in
  the AJ. 8 of 12 figures included, full paper at
 
 http://www.astro.lsa.umich.edu:80/users/philf/www/papers/list.html
\\
  Galaxy cluster mass distribution are potentially useful probes of $\Omega_0$
and the nature of the dark matter. Large clusters will distort the observed
shapes of background galaxies through gravitational lensing allowing the
measurement of the cluster mass distributions. In this paper we describe weak
statistical lensing measurements of the most luminous X-ray cluster known,
RXJ1347.5-1145 at z=0.45. We detect a shear signal in the background galaxies
at a signal-to-noise ratio of 7.5 in the radial range $120 \le r \le 1360
h^{-1}$ kpc. A mass map of the cluster reveals an 11$\sigma$ peak in the
cluster mass distribution consistent with the position of the central dominant
galaxy and 3 $\sigma$ evidence for the presence of a subcluster at a projected
radius of $1.3 - 1.7 h^{-1}$ Mpc from the cluster center. In the range 
$120 \le r \le 1360 h^{-1}$ kpc mass traces light, and the azimuthally averaged cluster
mass and light profiles are consistent with singular isothermal spheres with
M(r<1 Mpc) = $1.7 \pm 0.4 \times 10^{15} M_\odot$. Assuming an isotropic
velocity distribution function, the implied velocity dispersion is $\sigma =
1500 \pm 160 km s^{-1}$. The rest-frame mass-to-light ratio is $M/L_B = 200
\pm 50 h M_\odot/L_{B\odot}$. The lensing mass estimate is almost twice as
high as a previously determined X-ray mass estimate.
 ( http://xxx.lanl.gov/abs/astro-ph/9703189 ,  114kb)
\\


Paper: astro-ph/9606039
From: mellier@iap.fr (Yannick Mellier)
Date: Thu, 6 Jun 96 15:12:48 +0200

Title: DISTRIBUTION OF GALAXIES AT LARGE REDSHIFT AND COSMOLOGICAL PARAMETERS FROM MAGNIFICATION BIAS IN Cl0024+1654
Authors: B. Fort (1) Y. Mellier (2,1,3) M. Dantel-Fort Fort (1) ((1)
  Observatoire de Paris DEMIRM , (2) Institut d'Astrophysique de Paris, (3) UMR
  5572 Observatoire Midi Pyrenees.)
Comments: Latex, 11 pages, l-aa.sty and psfig.sty, 10 figures. 187K gzipped tar
  file. Submitted to Astronomy and Astrophysics Main Journal
\\
  We analyse the surface density of very faint galaxies at the limit of the sky
background noise in the field of the cluster of galaxies Cl0024+1654. The
radial variation of their number density in the magnitude bins $B=26-28$ and
$I=24-26.5$ displays an (anti)bias magnification effect for $I < 24$ which
provides the redshift range of the populations seen in $B$ and $I$. The
depletion curve can be reproduced with two redshift populations with $60\% \pm
10\%$ of the $B$ galaxies between $z=0.9$ and $z=1.1$ and the remaining at a
redshift close to $z=3$. The $I$ selected population is similar but with a
minimum extending from the $B$ inner critical line to $R_I=60"$. Whatever the
cosmological model, the $I$-selected galaxies spread up to a larger redshift
with about 20\% above $z > 4$. Using a model for the gravitational potential,
the locations of the two extreme critical lines for the B and I galaxies favour
$\Omega_{\Lambda}$-dominated flat universes with a cosmological
 constant ranging from 0.6 to 0.9. The result is confirmed by a preliminary
investigation of A370. We discuss the method to search the "last critical line"
and the various biases.
(http://xxx.lanl.gov/abs/astro-ph/9606039 ,  178kb)
\\


Paper: astro-ph/9608068
From: "Joshua Frieman" frieman@falstaff.fnal.gov
Date: Mon, 12 Aug 1996 20:54:04 -0500

Title: Weak Lensing and the Measurement of q0 from Type Ia Supernovae
Author: Joshua A. Frieman
Comments: 14 pages LaTeX with 2 figures; earlier version (Mar. '96) accepted
  for publication in Comments on Astrophysics. Also available by WWW at
  http://www-astro-theory.fnal.gov/Publications/00Index.html
Report-no: Fermilab-Pub-96/067-A
\\
  On-going projects to discover Type Ia supernovae at redshifts z = 0.3 - 1,
coupled with improved techniques to narrow the dispersion in SN Ia peak
magnitudes, have renewed the prospects for determining the cosmic deceleration
parameter $q_0$. We estimate the expected uncertainty in the Hubble diagram
determination of $q_0$ due to weak lensing by structure in the universe, which
stochastically shifts the apparent brightness of distant standard candles.
Although the results are sensitive to the density power spectrum on small
scales, the induced flux dispersion $\sigma_m < 0.04 \Omega_{m,0}^{1/2}$ mag 
for sources at $z \leq 0.5$, well below the ``intrinsic" spread of nearby SN Ia
magnitudes, $\sigma_M \simeq 0.2 mag$. Thus, density inhomogeneities do not
significantly impact the current program to measure $q_0$, in contrast to a
recent claim. If, however, light-curve shape and other calibrators can reduce
the effective intrinsic spread to 0.1 mag at high z, then weak lensing could
increase the observed spread by 30% in an Omega_{m,0}=1 universe for SNe at z >
1.
 (http://xxx.lanl.gov/abs/astro-ph/9608068 ,  20kb)
\\


Paper: astro-ph/9702061
From: "Takashi Okamura (Dep. of Phys.)" okamura@th.phys.titech.ac.jp
Date: Thu, 06 Feb 1997 21:27:37 +0900   (25kb)

Title: On the General Theorems about the Gravitational Lensing
Authors: Takeshi Fukuyama and Takashi Okamura
Comments: 8 pages, aastex, 2 figures
\\
  We study the general theorem about the gravitational lensing which says the
relationship between the numbers of images with different parities. Our
formulation allows an extension to the nontranparent and singular model.
 ( http://xxx.lanl.gov/abs/astro-ph/9702061 ,  25kb)
\\


Paper: astro-ph/9508071
From: Geza Gyuk gyuk@oddjob.uchicago.edu
Date: Wed, 16 Aug 1995 19:19:00 -0500
Date (revised): Wed, 16 Aug 1995 21:02:56 -0500

Title: GRAVITATIONAL MICROLENSING AND THE GALACTIC HALO
Authors: Evalyn I. Gates, Geza Gyuk, and Michael S. Turner
Comments: 19 pages, 13 multipart figures are available at

  ftp://astro.uchicago.edu/ftp/pub/astro/gyuk/
Report-no: FERMILAB--Pub--95/267-A
\\
  By means of extensive galactic modeling we study the implications of the more
than eighty microlensing events that have now been observed for the composition
of the dark halo of the Galaxy, as well as for other properties of the Galaxy.
We take the Galaxy to be comprised of luminous and dark disk components, a
bulge, and a dark halo consisting of both MACHOs and cold dark matter with each
component being described by several observationally motivated parameters. We
pare down an initial model space of millions of galactic models to viable
models, those which are consistent with the observational data, including
rotation curve, local projected mass density, and microlensing rates toward the
LMC and bulge. On the basis of a conservative, minimal set of observational
constraints an all-MACHO halo cannot yet be excluded, although in most viable
models of the Galaxy the halo MACHO fraction is between 0\% and 30\%,
consistent with expectations for a universe whose primary component is cold
dark matter. An all-MACHO halo is required to be light, and when data on the
local escape velocity and satellite-galaxy proper motions, which probe the
extent of the dark halo, are taken into account, models which have a high MACHO
mass fraction are ruled out. We also explore the possibility that there are no
MACHOs in the halo. Finally, we point out several important tests that could
definitively exclude an all-MACHO e.g., optical depth for microlensing which is
less than $1.5\times 10^{-7}$ toward the LMC or greater than $3\times 10^{-6}$
toward the bulge.
\\

Paper: astro-ph/9606104
From: Bernard S. Gaudi gaudi@payne.mps.ohio-state.edu
date: Mon, 17 Jun 96 14:26:18 EDT

Title: DETECTION RATES FOR CLOSE BINARIES VIA MICROLENSING
Authors: B. Scott Gaudi, Andrew Gould
Comments: 19 pages including 6 figures. Uses $phyyzx$ format. Send requests for
  higher quality figures to gaudi@payne.mps.ohio-state.edu
Report-no: OSU-TA-16/96
\\
  Microlensing is one of the most promising methods of reconstructing the
stellar mass function down to masses even below the hydrogen-burning limit. The
fundamental limit to this technique is the presence of unresolved binaries,
which can in principle significantly alter the inferred mass function. Here we
quantify the fraction of binaries that can be detected using microlensing,
considering specifically the mass ratio and separation of the binary. We find
that almost all binary systems with separations greater than $b \simeq 0.4$ of
their combined Einstein ring radius are detectable assuming a detection
threshold of $3\%$. For two M dwarfs, this corresponds to a limiting separation
of $\geq 1 AU$. Since very few observed M dwarfs have companions at
separations $\leq 1 AU$, we conclude that close binaries will probably not
corrupt the measurements of the mass function. We find that the detectability
depends only weakly on the mass ratio. For those events for which individual
masses can be determined, we find that binaries can be detected down to $b 
\simeq 0.2$.
(http://xxx.lanl.gov/abs/astro-ph/9606104 ,  74kb)
\\

Paper: astro-ph/9610123
From: B. Scott Gaudi gaudi@payne.mps.ohio-state.edu
Date: Wed, 16 Oct 96 07:05:30 EDT

Title: Planet Parameters in Microlensing Events
Authors: B. Scott Gaudi, Andrew Gould
Comments: 38 pages, 11 figures, TeX, uses PHYZZX, higher quality figures
  available upon request
Report-no: OSU-TA-26/96
\\
  A planetary microlensing event occurs when a planet perturbs one of the two
images created in a point-mass microlensing event, causing a deviation from the
standard Paczy\'nski curve. Determination of the two physical parameters that
can be extracted from a planetary microlensing event, the planet/star mass
ratio q, and the planet/star separation in units of the stellar Einstein
ring, $y_p$, is hampered by several types of degeneracies. There are two
distinct and qualitatively different classes of planetary events: major and
minor image perturbations. For major image perturbations, there is a
potentially crippling continuous degeneracy in q which is of order
$\delta_d^{-1}$, where $\delta_d$ is the maximum fractional deviation of the
planetary perturbation. Since the threshold of detection is expected to be
$\delta_d \simeq 5\%$, this degeneracy in q can be a factor of $\simeq 20$. For
minor image perturbations, the continuous degeneracy in q is considerably
less severe, and is typically less than a factor 4. We show that these
degeneracies can be resolved by observations from dedicated telescopes on
several continents together with optical/infrared photometry from one of these
sites. There also exists a class of discrete degeneracies. These are typically
easy to resolve given good temporal coverage of the planetary event.
Unambiguous interpretation of planetary microlensing events requires the
resolution of both types of degeneracy. We describe the degeneracies in detail
and specify the situations in which they are problematic. We also describe how
individual planet masses and physical projected separations can be measured.
 (http://xxx.lanl.gov/abs/astro-ph/9610123 ,  171kb)
\\

Paper: astro-ph/9701070
From: Matthias Bartelmann 

msb@MPA-Garching.MPG.DE
Date: Tue, 14 Jan 1997 14:13:20 +0100 (MET)

Title: Constraining the Mass Distribution of Cluster Galaxies by Weak Lensing
Author: Bernhard Geiger (MPA)
Comments: 10 pages, including 6 figures, Latex, uses lamuphys.sty, to appear in
  the proceedings of the ESO Workshop on Galaxy Scaling Relations: Origins,
  Evolution and Applications. Garching, 18-20 November 1996
\\
  Analysing the weak lensing distortions of the images of faint background
galaxies provides a means to constrain the mass distribution of cluster
galaxies and potentially to test the extent of their dark matter halos as a
function of the density of the environment. Here I describe simulations of
observational data and present a maximum likelihood method to infer the average
properties of an ensemble of cluster galaxies.
 (http://xxx.lanl.gov/abs/astro-ph/9701070 ,  224kb)
\\


Paper: astro-ph/9509149
From:Ortwin Gerhard gerhard@astro.unibas.ch
Date: Fri, 29 Sep 1995 09:36:43 +0100 (MET)

Title: BARYONIC DARK HALOS; MACHOS AND COLD GAS?
Authors: Ortwin Gerhard (Astron.Inst., Univ.Basel, CH) and Joseph Silk
  (Dpt.Astron. and Phys., Univ.Calif., Berkeley, USA)
Comments:13 pages, submitted to ApJ.Uuencoded, gzip-compressed ps-file
  including 2 figures.Also available at

  http://www.astro.unibas.ch/~gerhard/papers/dmmn.ps.gz.uu
Report-no: Astr.Inst.Basel Prep.Ser.84
\\
  We consider the possibility that the dark matter in the halos of galaxies may
be in the form of clusters of machos within which are embedded cold, dense
gas clouds. Microlensing experiments have found evidence that the Galactic halo
contains up to half of its mass in the form of low-mass macho s. A number of
observational and dynamical arguments point to the existence of hitherto
unobserved cold gas around galaxies. We show that the cold gas can be
stabilized by macho clusters. Within the framework of a simple two-component
model, we derive constraints on the macho clusters and on the halo cold gas
content. Typical cluster masses are $\sim 10 M_\odot$, typical macho masses are
$\sim 0.01 M_\odot$, and the gas content could be up to of order 50 \%. Various
predictions are given for testing the hypothesis that such objects could
constitute most of the mass in the dark halos of galaxies. If halos are indeed
baryonic and contain significant amounts of cold gas, they are likely to play a
much more active role in galaxy formation and evolution than is commonly
supposed. (astro-ph/9509149 ,  103kb)
\\


Paper: astro-ph/9601108
From: gioia@abell.IFA.Hawaii.Edu (Isabella gioia)
Date: Sat, 20 Jan 96 20:49:15 HST

Title: X-RAY SELECTED CLUSTERS OF GALAXIES
Author: Isabella M. Gioia (Institute for Astronomy, University of Hawaii,
  Honolulu, HI and Istituto di Radioastronomia del CNR, Bologna, Italy)
Comments: 5 pages
Report-no: IfA-95/65
\\
  This paper given at the meeting on "Mapping, Measuring and Modelling the
Universe" presents three topics: 1) the study of the clusters and groups of
galaxies found serendipitously in the North Ecliptic Pole (NEP) region of the
ROSAT all-sky survey; 2) the highest redshift clusters found in the EMSS (up to
z=0.82) and the cosmological implications of their very existence; 3) the
gravitational lensing in the EMSS X-ray selected clusters of galaxies observed
by the Hubble Space Telescope.
(http://xxx.lanl.gov/abs/astro-ph/9601108 ,  447kb)
\\


Paper: astro-ph/9610010
From: Paolo Gondolo gondolo@menuhin.berkeley.edu
Date: Tue, 1 Oct 1996 17:15:06 MDT

Title: AGAPE: a Microlensing Search for Dark Matter by Monitoring Pixels
Authors: P. Gondolo, R. Ansari, M. Auriere, P. Baillon, A. Bouquet, G.
  Coupinot, Ch. Coutures, C. Ghesquiere, Y. Giraud-Heraud, J. Hecquet, J.
  Kaplan, Y. Le Du, A.L. Melchior, M. Moniez, J.P. Picat, G. Soucail
Comments: presented at the International Conference on "Dark and Visible Matter
  in Galaxies" (Sesto Pusteria, Italy, 2-5 July 1996), 8 pages, 7 figures, uses
  paspconf.sty, psfig.sty
\\
  AGAPE is an observational search of massive compact halo objects (MACHOs) in
the direction of M31 by means of a novel method: the gravitational microlensing
of unresolved stars. The search consists in examining CCD pixel light curves
for microlensing features. The high level of temporal stability necessary to
detect microlensing events has been achieved, with quiet pixels stable within a
factor of two of the photon noise (the brightest ones down to a level of 0.001
mag). The data analysis is still in progress, but hundreds of variable objects
(cepheids, novae, ...) have already been found. Among them there are several
lightcurves that resemble microlensing events.
 (http://xxx.lanl.gov/abs/astro-ph/9610010 ,  100kb)
\\


Paper: astro-ph/9603148
From: Andrew P. Gould gould@payne.mps.ohio-state.edu
Date: Wed, 27 Mar 96 17:58:48 EST

Title: EXTREME MICROLENSING
Author: Andrew Gould
Comments: 17 pages
Report-no: OSU-TA-9/96
\\
  Extreme microlensing events, defined as events with maximum magnification
$A_\geq 200$ are a potentially powerful probe of the mass spectrum and
spatial distribution of objects along lines of sight toward the Galactic bulge.
About 75 yr${}^{-1}$ such events are expected for main-sequence sources with
$I_0<19$. For many of these it is possible to measure both a ``proper motion''
and a ``parallax'' which together would yield individual mass, distance, and
transverse-speed determinations of the lensing object. The proper motion is
determined from finite-source effects when the lens transits, or nearly
transits the source. The parallax is determined by observing the difference in
the light curve as seen from two Earth observatories separated by about 1 Earth
radius, $R_\oplus$. The size of the parallax effect is $\sim A_{max}
R_\oplus/ = r_e$ where $= r_e$ is the projected Einstein radius. This
can be of order 1\%. Detection of candidate events requires a pixel-lensing
search of the entire bulge once per day, preferably by at least two
observatories on different continents. Follow-up observation must be carried
using optical/infrared photometry, with short (e.g.\ 1 minute) exposures on
small ($\geq 1$ m) telescopes. Extreme microlensing observations toward the
Large Magellanic Cloud do not appear feasible at the present time.
(http://xxx.lanl.gov/abs/astro-ph/9603148 ,  50kb)
\\


Paper: astro-ph/9605105
From: Andrew P. Gould gould@payne.mps.ohio-state.edu
Date: Fri, 17 May 96 06:46:36 EDT

Title: LES MICROLENTILLES GRAVITATIONNELLES
Author: Andrew Gould
Comments: Four lectures given at College de France, Paris. 48 pages. Figures
  available separately
Report-no: LPC-96-23
\\
  Je presente une revue des microlentilles gravitationnelles en quatre lecons.
Dans un premier temps, je discute la theorie des microlentilles dans le
contexte general des lentilles, en incluant les effets de la taille finie des
sources, de la parallaxe, et du retard temporel entre les images. Dans la
deuxieme lecon, j'analyse les experiences courantes. Je montre qu'il n'est pas
possible d'expliquer les evenements observes avec les etoiles connues, que ce
soit en direction du bulbe ou du Grand Nuage de Magellan. Je decris quelques
nouvelles experiences qui pourraient nous reveler les caracteristiques des
objets detectes. Le troisieme sujet porte sur la methode des pixels, inventee
pour observer des evenements de microlentilles sur des sources non resolues. Je
presente une analyse generale de la methode, en incluant des problemes
d'alignement geometrique, photometrique, et de PSF, du rapport signal sur
bruit, et de la nature des informations tirees des observations. Je presente un
rapport sur le progres des experiences actuelles et je discute de deux idees
pour rechercher des objets sombres dans l'amas de Virgo et des `microlentilles
extremes' dans le bulbe. Pour finir, je parle de l'avenir des microlentilles.
J'explique comment on peut les utiliser pour rechercher des planetes, pour
mesurer les vitesses transverses de galaxies et les vitesses de rotation
d'etoiles geantes, et pour rechercher les objets de la masse d'une comete se
trouvant de l'autre cote de l'univers. Ce texte est publie sous forme de
rapport interne du Laboratoire de Physique Corpusculaire du College de France
(LPC 96-23). Il inclue une copie des transparents de ces quatres lecons, copie
disponible aupres de Daniele Levaillant: levaillant@cdf.in2p3.fr
(http://xxx.lanl.gov/abs/astro-ph/9605105 ,  35kb)
\\


Paper: astro-ph/9608045
From: Andrew P. Gould gould@payne.mps.ohio-state.edu
Date: Fri, 9 Aug 96 14:44:34 EDT

Title: The Hollywood Strategy for Microlensing Detection of Planets
Author: Andrew Gould
Comments: 6 pages, no figures, Talk given at the 12th IAP Colloquium: Variable
  Stars and the Astrophysical Returns of Microlensing Surveys
Report-no: OSU-TA-19/96
\\
  Follow the big stars! I review the theory of detection and parameter
measurement of planetary systems by follow-up observations of ongoing
microlensing events. Two parameters can generically be measured from the event
itself: the planet/star mass ratio, $q$, and the planet/star separation in
units of the Einstein ring. I emphasize the advantages of monitoring events
with giant-star sources which are brighter (thus easier to monitor) and bigger
(thus offering the prospect of measuring an additional parameter from
finite-source effects: the proper motion $\mu$). There is potentially a strong
degeneracy between $q$ and $\mu$. I present a simple analytic representation of
this degeneracy. I then describe how it can be broken using accurate
single-band photometry from observatories around the world, or optical/infrared
photometry from a single site, or preferably both. Both types of observations
are underway or will be soon. Monitoring of giant-star events seen toward the
bulge is also the best way to determine the content and structure of the inner
Galaxy.
 (http://xxx.lanl.gov/abs/astro-ph/9608045 ,  9kb)
\\


Paper: astro-ph/9611057
From: Andrew P. Gould gould@payne.mps.ohio-state.edu
Date: Thu, 7 Nov 96 10:02:03 EST

Title: Measuring the Rotation Speed of Giant Stars From Gravitational
  Microlensing
Author: Andrew Gould
Comments: 11 pages including 1 embedded figure
Report-no: OSU-TA-29/95
\\
  During some gravitational lensing events, the lens transits the face of the
star. This causes a shift in the apparent radial velocity of the star which is
proportional to its rotation speed. It also changes the magnification relative
to what would be expected for a point source. By measuring both effects, one
can determine the rotation parameter $v\sin i$. The method is especially useful
for K giant stars because these have turbulent velocities that are typically
large compared with their rotation speed. By making a series of radial velocity
measurements, one can typically determine $v\sin i$ to the same accuracy as the
individual radial velocity measurements. There are approximately 10
microlensing transit events per year which would be suitable to make these
measurements.
 (http://xxx.lanl.gov/abs/astro-ph/9611057 ,  14kb)
\\


Paper: astro-ph/9611136
From: "Andrew P. Gould" <gould@payne.mps.ohio-state.edu>
Date: Mon, 18 Nov 96 10:07:35 EST

Title: Microlensing: Prospects for the Future
Author: Andrew Gould
Comments: from Sheffield workshop on Identification of Dark Matter, 12 p
Report-no: OSU-TA-30/96
\\
  Four ongoing microlensing experiments have produced important new results but
also big puzzles, the major one being that the expected classes of lenses
cannot account for the observed distribution of time scales. I discuss future
experiments that could resolve these puzzles. By far the most important would
be to launch a parallax satellite into solar orbit. I also discuss a number of
non-dark-matter applications of microlensing, including searching for planets,
measuring the rotation speeds of giant stars, and imaging a black hole at the
center of a quasar.
 (http://xxx.lanl.gov/abs/astro-ph/9611136 ,  14kb)
\\


Paper: astro-ph/9703050
From: "Andrew P. Gould" gould@payne.mps.ohio-state.edu
Date: Sun, 9 Mar 97 10:51:14 EST   (25kb)

Title: Microlensing: Current Results and Future Prospects
Authors: Andrew Gould
Comments: Talk given at 25th Anniversary of Wise Observatory. 11 pages
Report-no: OSU-TA-5/97
\\
  The initial results of microlensing surveys toward the Galactic bulge and the
LMC are puzzling. Toward the LMC, the total mass in MACHOs is of order half
that required to explain the dark matter, but the estimated MACHO mass (~0.4
Msun) is most consistent with stars that should have been seen. Toward the
bulge, the total mass is consistent with that given by dynamical estimates of
the bulge mass, but the observed timescales seem to require that a large
fraction of the bulge is made of brown dwarfs. I discuss possible experiments
to resolve these puzzles. I also discuss several applications of microlensing
to non-dark-matter problems including searching for planets and imaging the
black hole at the center of a quasar with $10^{-10}$ arcsec resolution.
 ( http://xxx.lanl.gov/abs/astro-ph/9703050 ,  25kb)
\\


Paper: astro-ph/9611185
From: "Andrew P. Gould" gould@payne.mps.ohio-state.edu
Date: Fri, 22 Nov 96 05:46:19 EST

Title: Star Counts From HST: Implications for Dark Matter
Author: Andrew Gould
Comments: from Sheffield workshop on Identification of Dark Matter, 4 p
Report-no: OSU-TA-32/96
\\
  Star counts made with the Hubble Space Telescope (HST) probe four populations
that are important for dark matter: disk, halo, bulge, and intergalactic. The
disk mass function falls for masses M<0.6 Msun in sharp contrast to the rising
Salpeter function usually assumed. The amount of ``observed'' disk material is
therefore lower than commonly believed which implies the need for disk dark
matter. Halo stars contribute no more than a few percent of the dark matter.
Disk and halo together contribute no more than 10% of the observed
microlensing optical depth toward the Large Magellanic Cloud. The bulge
luminosity function is similar to that of the disk down to $M_V ~ 10$. If this
similarity continues to the bottom of the main sequence, the bulge microlensing
events can only be explained by a large population of brown dwarfs.
Intergalactic stars in the Local Group have a density lower than the local halo
density by at least $10^{-3.5}$.
 (http://xxx.lanl.gov/abs/astro-ph/9611185 ,  7kb)
\\


Paper: astro-ph/9606003
From: Andrew P. Gould gould@payne.mps.ohio-state.edu
Date: Mon, 3 Jun 96 10:59:44 EDT

Title: FEMTOLENS IMAGING OF A QUASAR CENTRAL ENGINE USING A DWARF STAR
Authors: Andrew Gould and B. Scott Gaudi
Comments: 12 pages including 3 embedded figures
Report-no: OSU-TA-13/96
\\
  We show that it is possible to image the structure of a distant quasar on
scales of $\sim 1\,$AU by constructing a telescope which uses a nearby dwarf
star as its ``primary lens'' together with a satellite-borne ``secondary''. The
image produced by the primary is magnified by $\sim 10^5$ in one direction but
is contracted by 0.5 in the other, and therefore contains highly degenerate
one-dimensional information about the two-dimensional source. We discuss
various methods for extracting information about the second dimension including
``femtolens interferometry'' where one measures the interference between
different parts of the one-dimensional image with each other. Assuming that the
satellite could be dispatched to a position along a star-quasar line of sight
at a distance $r$ from the Sun, the nearest available dwarf-star primary is
likely to be at $\sim 15\,\pc\,(r/40\,\rm AU)^{-2}$. The secondary should
consist of a one-dimensional array of mirrors extending $\sim 700\,$m to
achieve 1 AU resolution, or $\sim 100\,$m to achieve 4 AU resolution.
(http://xxx.lanl.gov/abs/astro-ph/9606003 ,  49kb)
\\


Paper: astro-ph/9612144
From: "Andrew P. Gould" gould@payne.mps.ohio-state.edu
Date: Sat, 14 Dec 96 08:51:30 EST

Title: Signatures of Accretion Disks in Quasar Microlensing
Authors: Andrew Gould and Jordi Miralda-Escude
Comments: 11 pages plus 1 postscript figure
Report-no: OSU-TA-33/96
\\
  We propose that relative variability on short time-scales of the multiple
images of a lensed quasar, after removal of the time delay, may be caused by
hot spots or other moving structures in the accretion disk crossing microlens
caustics caused by stellar mass objects in the lensing galaxy. Such variability
has been reported in the two images of 0957+561. The short durations would be
due to the high rotation speed of the disk (v/c ~ 0.1), rather than planetary
mass objects in the slowly moving (v/c ~ 0.001) lens. This interpretation could
be confirmed by finding periodicity, or correlations of the spectral and flux
variations due to the Doppler effect in the disk. We also propose another
signature of stationary accretion disks (with no intrinsic variability): the
gradient of the magnification over the accretion disk should cause a relative
color change between the images whose sign and amplitude are correlated with
the time derivative of the flux difference between the images. Other color
terms induced by the radial variation of disk colors are of second order in the
magnification gradient. The methods proposed here can be used first to verify
that accretion disks near supermassive black holes are the source of the
continuum radiation from quasars, and then to study them.
 (http://xxx.lanl.gov/abs/astro-ph/9612144 ,  32kb)
\\


Paper: astro-ph/9510089
From: griest@astrophys.ucsd.edu (Kim Griest)
Date: Tue, 17 Oct 95 17:51:18 PDT
Date (revised): Tue, 17 Oct 95 18:05:14 PDT

Title: THE NATURE OF DARK MATTER
Author: Kim Griest
Comments: 32 pages, uuencoded, compressed, tarred plain tex file, with 9
  postscript figures included. Lectures presented at the International School
  of Physics ``Enrico Fermi" Course ``Dark Matter in the Universe", Varenna, 25
  July - 4 August, 1995. To appear in the proceedings
\\
  We review some recent determinations of the amount of dark matter on galactic
and larger scales, with special attention to the dark matter in the Milky Way.
We then briefly review the motivation for and basic physics of several dark
matter candidates, and then go into more depth for two candidates, the
neutralino from supersymmetry, and the baryonic Macho candidate. We give some
motivation for supersymmetry and review neutralino detection strategies. For
Machos we give a description of the discovery of Machos via gravitational
microlensing and the interpretation of the results with respect to the dark
matter problem. (astro-ph/9510089 ,  129kb + 592kb)
\\


Paper: astro-ph/9506016
From: griest@astrophys.ucsd.edu (Kim Griest)
Date: Fri, 2 Jun 95 13:14:42 PDT

Title: MACHO COLLABORATION SEARCH FOR BARYONIC DARK MATTER VIA GRAVITATIONAL
  MICROLENSING
Author: K. Griest, C. Alcock, R.A. Allsman, T.S. Axelrod, D.P. Bennett, K.H.
  Cook, K.C. Freeman, J. Guern, M. Lehner, S.L. Marshall, S. Perlmutter, B.A.
  Peterson, M.R. Pratt, P.J. Quinn, A.W. Rodgers, C.W. Stubbs, W. Sutherland,
  D. Welch (The MACHO Collaboration)
Comments: 18 Pages, figures included. To appear in the proceeding of the
  Pascos/Hopkins Symposium, Baltimore, Maryland 1995. uuencoded, tarred,
  compressed postscript
\\
  Results are presented from the MACHO collaboration gravitational microlensing
search. The experiment and the nearly 50 microlensing events that have been
detected are described. Limits on the baryonic content of the halo are given,
as are estimates of the Macho contribution to the dark halo. Optical depths
toward the bulge, and several unusual events such as a binary lens and a
parallax event are discussed. Possible interpretations of these results are
also discussed.
\\


Paper: astro-ph/9607134
From: Geza Gyuk gyuk@oddjob.uchicago.edu
Date: Thu, 25 Jul 1996 15:32:33 -0500

Title: GRAVITATIONAL MICROLENSING AND THE STRUCTURE OF THE INNER MILKY WAY
Authors: Geza Gyuk (Univ. Chicago)
Comments: 32 pages, Sixteen figures available at
  ftp://astro.uchicago.edu/pub/astro/gyuk/micromap/
\\
  We analyze the first-year MACHO collaboration observations of microlensing
towards the Galactic center using a new direct likelihood technique that is
sensitive to the distribution of the events on the sky. We consider the full
set of 41 events, and calculate the direct likelihood against a
simply-parameterized Galactic model consisting of either a gaussian or
exponential bar and a double exponential disk. Optical depth maps are
calculated taking into account the contribution of both disk lenses and
sources. We show that based on the presently available data, a slope in the
optical depth has been clearly detected ($3\sigma$) in Galactic latitude and
that there are indications of a small slope in Galactic longitude. We discuss
limits that can be set on the mass, angle and axis ratio of the Galactic bulge.
We show that based on microlensing considerations alone, $M_{Bulge}>1.5\times
10^{10} M_{odot}$ at the 90\% confidence level and that the bulge inclination angle
is less than $30 \deg$ also at the 90\% confidence level. The mostly likely bar
mass is $M_{Bulge}=3.5\times10^{10} M_{odot}$. Such a high mass would imply a low
MACHO fraction for the halo. We consider disk parameters and show that there
are two degeneracies between the effects of a disk and those of a bar on the
optical depths. Finally, we discuss how to break these degeneracies and
consider various strategies for future microlensing observations.
 (http://xxx.lanl.gov/abs/astro-ph/9607134 ,  23kb)
\\
 

Paper: astro-ph/9607080
From: Deborah Becker Haarsma 

dhaarsma@maggie.mit.edu
Date: Tue, 16 Jul 96 19:13:41 EDT

Title: THE 6cm LIGHT CURVES OF B0957+561, 1979-1994: NEW FEATURES AND IMPLICATIONS FOR THE TIME DELAY
Authors: Deborah B. Haarsma (MIT), Jacqueline N. Hewitt (MIT), Joseph Leh\'ar
  (CfA), and Bernard F. Burke (MIT)
Comments: Submitted to Astrophysical Journal. 36 pages; aaspp LaTex plus 15
  postscript figures. Hard copies available on request
  (dhaarsma@maggie.mit.edu), also available by anonymous ftp to
  ftp://zenobia.mit.edu/pub/dhaarsma
\\
  We report on 15 years of VLA monitoring of the gravitational lens B0957+561
at 6 cm. Since our last report in 1992, there have been 32 additional
observations, in which both images have returned to their quiescent flux
density levels and the A image has brightened again. We estimate the time delay
from the light curves using three different techniques: the $\chi^2$ analysis
of Press, Rybicki, and Hewitt (1992a,b), the dispersion analysis of Pelt et al.
(1994, 1996), and the locally normalized discrete correlation function of
Leh\'ar et al. (1992). Confidence intervals for these time delay estimates are
found using Monte Carlo techniques. With the addition of the new observations,
it has become obvious that some observations from Spring 1990 are not
consistent with the statistical properties of the rest of the light curves, so
we analyze the light curves with those points removed, as well as the complete
light curves. The new features in the light curve show that the time delay is
less than 500 days, in contrast with analysis of earlier versions of the radio
light curves. The three statistical techniques applied to the two versions of
the data set show that the time delay is in the range 375 to 485 days (or 1.03
to 1.33 years, A leading B), and the flux ratio is in the range 0.695 to 0.707
(B/A).
(http://xxx.lanl.gov/abs/astro-ph/9607080 ,  337kb)
Paper: astro-ph/9607080
replaced with revised version Tue, 26 Nov 96 11:55:25 EST

Title: The 6 cm Light Curves of B0957+561, 1979-1994: New Features and
  Implications for the Time Delay
Authors: Deborah B. Haarsma (MIT), Jacqueline N. Hewitt (MIT), Joseph Leh\'ar
  (CfA), and Bernard F. Burke (MIT)
Comments: To appear in The Astrophysical Journal, April 10, 1997. Changes in
  discussion section and Table 1. 37 pages, including 15 postscript figures.
  Also available at http://space.mit.edu/RADIO/papers.html
\\ (http://xxx.lanl.gov/abs/astro-ph/9607080 ,  324kb)
For general information on the new physics archive (partitioned by
keyword subject classification), see 

http://xxx.lanl.gov/new/
For subscribe options to combined physics archives,
e-mail To: physics@xxx.lanl.gov, Subject: subscribe
\\


Paper: astro-ph/9703136
From: Takashi Hamana 

hamana@astroa.astr.tohoku.ac.jp
Date: Fri, 21 Mar 1997 20:14:44 +0900   (634kb)

Title: Lensing Effects on the Protogalaxy Candidate cB58 and their Implications
  for the Cosmological Constant
Authors: T. Hamana (1), M. Hattori (1), H. Ebeling (2), J. P. Henry (2), T.
  Futamase (1) and Y. Shioya (1) ((1) Astronomical Institute, Tohoku
  University, (2) Institute for Astronomy, University of Hawaii)
Comments: LaTex, 9 pages, 9 figures, uses aas2pp4.sty, Accepted for publication
  in ApJ
\\
  The amplification of the protogalaxy candidate cB58 due to gravitational
lensing by the foreground cluster of galaxies MS1512.4+3647 is quantified based
on recent ROSAT and ASCA X-ray observations. It is found that the amplification
is at most 25 for any reasonable cosmological model with or without
cosmological constant. It is also argued that the system may be used to place
new constraints on the value of the cosmological constant. The gas mass
fraction for this cluster is found to be about 0.2.
 ( http://xxx.lanl.gov/abs/astro-ph/9703136 ,  159kb)
\\


Paper: astro-ph/9610207
From: Francois Hammer 

Francois.Hammer@gin.obspm.fr
Date: Fri, 25 Oct 1996 19:43:12 +0100 (MET)

Title: Detailed lensing properties of the MS2137-2353 core and reconstruction
  of sources
Authors: F. Hammer, P. Teyssandier, E. J. Shaya, I. M. Gioia, G. A. Luppino and
  O. Le F\`evre
Comments: 12 pages,Latex, available at 

ftp://gin.obspm.fr/depot/hammer ,
  Submitted to ApJ Letter
\\
  A deep HST image of the MS 2137-2353 core has revealed detailed morphological
structures in two arc systems, which are modelled and well reproduced after a
complete analysis of the lensing properties of the dark matter component.
Latter could have a simple elliptical mass distribution with ellipticity and
angular orientation similar to those of the visible and X-ray light, which
suggests that the MS 2137-2353 is a relaxed cluster at z=0.313. The predicted
density profile ($\rho$ $\sim$ $r^{-1.56\pm0.1}$ with $r_{c}$ $\le$
22.5$h_{50}^{-1}$ kpc) within 150$h_{50}^{-1}$ kpc implies increasing M/L ratio
with the radius, and could be in agreement with predictions from standard CDM
simulations. At least two faint sources (unlensed magnitude, R=23.9 and 26,
respectively) are aligned with the cluster core and are responsible of the arc
systems. They have been reconstructed with details as small as 0".02 (or
160$h_{50}^{-1}$ pc in the source assumed at z= 1), one could be a nearly
edge-on barred spiral galaxy, and the other has a more complex morphology,
which could be related to a close interacting pair and/or to dust. They show
strong signs of star formation indicated by compact HII regions well off their
center. The observation of giant luminous arcs by HST could even resolve the
size of giant HII regions at z$\sim$ 1.
 (http://xxx.lanl.gov/abs/astro-ph/9610207 ,  123kb)
\\


Paper: astro-ph/9608008
From: Han Cheongho cheongho@payne.mps.ohio-state.edu
Date: Thu, 1 Aug 96 14:39:43 EDT

Title: THE EFFECTS OF AMPLIFICATION BIAS IN GRAVITATIONAL MICROLENSING EXPERIMENT
Author: Cheongho Han
Comments: 16 pages including 4 figures, ApJ, submitted
Report-no: OSU-TA-18/96
\\
  Although a source star is fainter than the detection limit imposed by
crowding, it is still possible to detect an event if the star is located in the
seeing disk of a bright star is and gravitationally amplified: amplification
bias. Using a well-constrained luminosity function, I show that $\sim 40\%$ of
events detected toward the Galactic bulge are affected by amplification bias
and the optical depth might be overestimated by a factor $\sim 1.7$. In
addition, I show that if one takes amplification bias into consideration, the
observed time scale distribution matches significantly better, especially in
the short time-scale region, with the distribution expected from a
mass-spectrum model in which lenses are composed of the known stellar
population plus an additional population of brown dwarfs than it is without the
effect of the amplification bias
 (http://xxx.lanl.gov/abs/astro-ph/9608008 ,  36kb)
\\


Paper: astro-ph/9604031
From: Han Cheongho cheongho@payne.mps.ohio-state.edu
Date: Fri, 5 Apr 96 15:07:09 EST

Title: DETERMINATION OF THE EINSTEIN RING RADIUS FROM A BINARY-SOURCE EVENT
Author: Cheongho Han and Andrew Gould (The Ohio State University)
Comments: 15 pages including 1 table and 3 figures
Report-no: OSU-TA-11/96
\\
  We show that the Einstein ring radius and transverse speed of a lens
projected on the source plane, $\hat{r}_{\rm e}$ and $\hat{v}$, can be
determined from the light curve of a binary-source event, followed by the
spectroscopic determination of the orbital elements of the source stars. The
determination makes use of the same principle that allows one to measure the
Einstein ring radii from finite-source effects. For the case when the orbital
period of the source stars is much longer than the Einstein time scale, $P\gg
t_{\rm e}$, there exists a single two-fold degeneracy in determining
$\hat{r}_{\rm e}$. However, when $P \leq t_{\rm e}$ the degeneracy can often
be broken by making use of the binary-source system's orbital motion. Once
$\hat{r}_{\rm e}$, and thus $\hat{v}$ are determined, one can distinguish
self-lensing events in the Large Magellanic Cloud from Galactic halo events. In
addition, we propose to include eclipsing binaries as sources for gravitational
lensing experiments.
(http://xxx.lanl.gov/abs/astro-ph/9604031 ,  55kb)
\\


Paper: astro-ph/9702097
From: Avi Loeb loeb@cfata1.harvard.edu
Date: Tue, 11 Feb 1997 14:32:33 -0500   (79kb)

Title: Microlensing of an Elliptical Source by a Point Mass
Authors: David Heyrovsky and Abraham Loeb (Harvard University)
Comments: 25 pages, 9 figures, submitted to ApJ
\\
  We present an efficient method for computing lightcurves of an elliptical
source which is microlensed by a point mass. The amplification of an extended
source involves a two-dimensional integral over its surface brightness
distribution. We show that for a general surface brightness profile with an
elliptical symmetry, this integral can be reduced to one dimension. We derive
analytical results for the entire lightcurve in the limit of low (e.g.
planetary) mass lenses, and for the wings of all microlensing lightcurves in
general. In both cases, the lightcurve carries information about deviations of
the source from elliptical symmetry, e.g. due to spots. The method is used to
find the amplification of a circular red giant photosphere and an inclined
accretion disk. We demonstrate that microlensing of an emission line from a
disk can be used to infer the disk velocity structure and surface brightness
profile.
 ( http://xxx.lanl.gov/abs/astro-ph/9702097 ,  79kb)
\\


Paper: astro-ph/9611077
From: Bhuvnesh Jain bjain@MPA-Garching.MPG.DE
Date: Mon, 11 Nov 1996 22:18:14 +0100

Title: Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear
  Regimes
Authors: Bhuvnesh Jain (MPA) and Uros Seljak (CfA)
Comments: 35 pages, 10 figures included; submitted to ApJ
Report-no: MPA Preprint, November 1996
\\
  Weak lensing by large scale structure induces correlated ellipticities in the
images of distant galaxies. The two-point correlation is determined by the
matter power spectrum along the line of sight. We use the fully nonlinear
evolution of the power spectrum to compute the predicted ellipticity
correlation. We present results for different measures of the second moment for
angular scales $\theta \simeq$ 1'-3 degrees and for alternative normalizations of
the power spectrum, in order to explore the best strategy for constraining the
cosmological parameters. Normalizing to observed cluster abundance the rms
amplitude of ellipticity within a 15' radius is $\simeq 0.01 z_s^{0.6}$, almost
independent of the cosmological model, with $z_s$ being the median redshift of
background galaxies.
  Nonlinear effects in the evolution of the power spectrum significantly
enhance the ellipticity for $\theta <$ 10' -- on 1' the $rms$ ellipticity is $\simeq
0.05$, which is nearly twice the linear prediction. This enhancement means that
the signal to noise for the ellipticity is only weakly increasing with angle
for 2'$< \theta < $2 degrees, unlike the expectation from linear theory that it
is strongly peaked on degree scales. The scaling with cosmological parameters
also changes due to nonlinear effects. By measuring the correlations on small
(nonlinear) and large (linear) angular scales, different cosmological
parameters can be independently constrained to obtain a model independent
estimate of both power spectrum amplitude and matter density $\Omega_m$.
Nonlinear effects also modify the probability distribution of the ellipticity.
Using second order perturbation theory we find that over most of the range of
interest there are significant deviations from a normal distribution.
 (http://xxx.lanl.gov/abs/astro-ph/9611077 ,  82kb)
\\


Paper: astro-ph/9601122
From: MASSO@IFAE.ES
Date: Tue, 23 Jan 1996 12:52:25 GMT+0100

Title: MICROLENSING IMPLICATIONS FOR HALO DARK MATTER
Authors: Philippe Jetzer (PSI, Villigen, and Institute of Theoretical Physics,
  Univ. of Zurich) and Eduard Masso (IFAE and Dep. Fisica, Univ. Autonoma de
  Barcelona)
Comments: Six pages. Two figures (they can be telefaxed by request to
  masso@ifae.es). Talk at the second workshop on "The dark side of the
  Universe: experimental efforts and theoretical frameworks" (Rome, 13-14
  November 1995)
Report-no: Zurich University ZU-TH 1/96
\\
  The most accurate way to get information on the mass of the MACHOs (Massive
Astrophysical Compact Halo Objects) is to use the method of mass moments. For
the microlensing events detected so far by the EROS and the MACHO
collaborations in the Large Magellanic Cloud the average mass turns out to be
0.08$M_{\odot}$. Assuming a spherical standard halo model we find that MACHOs
contribute about 20\% to the halo dark matter. The eleven events recorded by
OGLE, mainly during its first two years of operation, in the galactic bulge
lead to an average mass of 0.29$M_{\odot}$, whereas forty events detected by
MACHO during its first year give 0.16$M_{\odot}$, thus suggesting that the lens
objects are faint disk stars.
 (http://xxx.lanl.gov/abs/astro-ph/9601122 ,  6kb)
\\


Paper: astro-ph/9611218
From: mike@mrao.cam.ac.uk
Date: Tue, 26 Nov 96 17:50 GMT

Title: Detection of a CMB decrement towards the z = 3.8 quasar pair
  PC1643+4631A and B
Authors: Michael E. Jones(1), Richard Saunders(1), Joanne C. Baker(1), Garret
  Cotter(1), Alastair Edge(2), Keith Grainge(1), Toby Haynes(1), Anthony
  Lasenby(1), Guy Pooley(1), Huub Rottgering(3)((1)MRAO Cambridge UK, (2)IoA
  Cambridge UK (3)Leiden Observatory)
Comments: 8 pages, LaTeX, 2 PostScript figures. To appear in Astrophysical
  Journal Letters
\\
  In a 15-GHz Ryle-Telescope observation of PC1643+4631 A and B, a pair of
quasars at redshifts z = 3.79 and 3.83 separated by 198 arcsec on the sky, we
find a decrement in the cosmic microwave background (CMB) of -380 +/- 64 uJy in
a 110 arcsec x 175 arcsec beam. Assuming this to be a Sunyaev-Zel'dovich effect
due to an intervening cluster, the minimum magnitude of the central temperature
decrement is 560 uK. A serendipitous ROSAT observation shows that there is no
X-ray-luminous cluster in the direction of the decrement at z < 1. The implied
gas mass is $>~ 2 x 10^{14}$ solar masses (assuming a temperature of ~ 5 keV),
indicating a total mass of $> 10^{15}$ solar masses. This result demonstrates the
existence of a massive system too distant to be detected by its emission, but
which can be found via its imprint on the CMB.
 (http://xxx.lanl.gov/abs/astro-ph/9611218 ,  28kb)
\\


Paper: astro-ph/9507075
From: Takashi Okamura Dep. of Phys,Tokyo.Inst. of Tech. okamura@th.phys.titech.ac.jp
Date: Thu, 20 Jul 1995 19:56:18 +0900
Date (revised): Thu, 20 Jul 1995 21:34:35 +0900

Title: GRAVITATIONAL LENSING AND CATASTROPHE THEORY
Authors: Y. Kakigi, T. Okamura and T. Fukuyama
Comments: 24 pages, latex, 18 figures
\\
  Singularities of caustics appeared in gravitational lensing effect are
discussed analytically. Multipole expansion model of lensing object is mainly
studied since it is tractable and universal. Our analyses are confirmed by
numerical calculations and applied to multiple quasar system of PG1115+080.
Consistencies with elliptical lens models are also discussed.
\\


Paper: astro-ph/9610120
From: Nick Kaiser 

kaiser@cita.utoronto.ca
Date: Tue, 15 Oct 1996 20:22:18 -0400 (EDT)

Title: Weak Lensing and Cosmology
Author: Nick Kaiser (CITA, U. Toronto)
Comments: 15 pages, submitted to Astrophysical Journal
  http://www.cita.utoronto.ca/~kaiser for related papers/links
Report-no: CITA-96-16
\\
  We explore the dependence of weak lensing phenomena on the background
cosmology. We first generalise the relation between $P_\psi(\omega)$, the
angular power spectrum of the distortion, and the power spectrum of density
fluctuations to non-flat cosmologies. We then compute $P_\psi$ for various
illustrative models. A useful cosmological discriminator is the growth of
$P_\psi$ with source redshift which is much stronger in low matter density
models, and especially in $\Lambda$-dominated models. With even crude redshift
information (say from broad band colours) it should be possible to constrain
the cosmological world model. The amplitude of $P_\psi(\omega)$ is also quite
sensitive to the cosmology, but requires a reliable external normalisation for
the mass fluctuations. If one normalises to galaxy clustering, with $M/L$ fixed
by small-scale galaxy dynamics, then low density models predict a much stronger
distortion. If, however, one normalises to large-scale bulk-flows, the
predicted distortion for sources at redshifts $Z_s \sim 1-3$ is rather
insensitive to the background cosmology. The signals predicted here can be
detected at a very high level of significance with a photometric survey
covering say 10 square degrees, but sparse sampling is needed to avoid large
sampling variance and we discuss the factors influencing the design of an
optimum survey. Turning to weak lensing by clusters we find that for high lens
redshifts ($Z_l\simeq1$) the critical density is substantially reduced in
$\Lambda$ models, but that the ratio of the shear or convergence to the
velocity dispersions or X-ray temperature of clusters is only very weakly
dependent on the cosmology.
 (http://xxx.lanl.gov/abs/astro-ph/9610120 ,  107kb)
\\


Paper: astro-ph/9611216
From: C. R. Keeton ckeeton@mars.harvard.edu
Date: Tue, 26 Nov 1996 10:34:30 MST

Title: Determining the Hubble Constant from the Gravitational Lens PG 1115+080
Authors: C. R. Keeton, C. S. Kochanek (Harvard-Smithsonian Center for
  Astrophysics)
Comments: 28 pages, 7 Postscript figures, submitted to ApJ
\\
  The quadruple gravitational lens PG 1115+080 cannot be fit by a single
ellipsoidal mass distribution, but it can be well fit by adding a perturbation
from the nearby group of galaxies. With the existing constraints, there are
degeneracies in the models with respect to the radial profiles of the galaxy
and the group and with respect to the position of the group, so that a wide
range of models give fits with $\chi^2/N_{DOF} < 1$. We find $H_0=60 \pm 17
km/s/Mpc (1\sigma)$ for a reasonable range of models. Smaller uncertainties in
$H_0$ can be achieved by reducing the standard errors in the lens galaxy position
from 50 mas to 10 mas, by reducing the the uncertainties in the time delays
from 3.4 days to 0.5 days, and by constraining the lens mass distribution using
HST photometry and the fundamental plane.
 (http://xxx.lanl.gov/abs/astro-ph/9611216 ,  274kb)
\\


Paper: astro-ph/9610163
From: Uros Seljak uros@cfata1.harvard.edu
Date: Mon, 21 Oct 1996 14:56:11 -0400

Title: Shear and Ellipticity in Gravitational Lenses
Authors: C.R. Keeton, C.S. Kochanek and U. Seljak
Comments: 38 pages, 9 figures, submitted to ApJ
\\
  Galaxies modeled as singular isothermal ellipsoids with an axis ratio
distribution similar to the observed axis ratio distribution of E and S0
galaxies are statistically consistent with both the observed numbers of
two-image and four-image lenses and the inferred ellipticities of individual
lenses. However, no four-image lens is well fit by the model (typical
$\chi^2/N_{dof} \sim 20$), the axis ratio of the model can be significantly
different from that of the observed lens galaxy, and the major axes of the
model and the galaxy may be slightly misaligned. We found that models with a
second, independent, external shear axis could fit the data well (typical
$\chi^2/N_{dof} \sim 1$), while adding the same number of extra parameters to
the radial mass distribution does not produce such a dramatic improvement in
the fit. An independent shear axis can be produced by misalignments between the
luminous galaxy and its dark matter halo, or by external shear perturbations
due to galaxies and clusters correlated with the primary lens or along the line
of sight. We estimate that the external shear perturbations have no significant
effect on the expected numbers of two-image and four-image lenses, but that
they can be important perturbations in individual lens models. However, the
amplitudes of the external shears required to produce the good fits are larger
than our estimates for typical external shear perturbations (10-15% shear
instead of 1-3% shear) suggesting that the origin of the extra angular
structure must be intrinsic to the primary lens galaxy in most cases.
 (http://xxx.lanl.gov/abs/astro-ph/9610163 ,  265kb)
\\


Paper: astro-ph/9610070
From: Eamonn Kerins kerins@wirtz.u-strasbg.fr
Date: Thu, 10 Oct 1996 07:17:45 MDT

Title: Zero-metallicity VLM stars as halo dark matter
Authors: E. J. Kerins
Comments: 11 pages incl. 4 figures. Submitted to A and A. Latex processing requires
  A and A style file (l-aa.sty) and epsf.sty for the figures (both macros can be
  obtained from http://xxx.lanl.gov/ftp/hep-th/papers/macros/ ). Postscript and
  dvi+figures versions can be obtained via anonymous ftp to
  
ftp://cdsxba.u-strasbg.fr/pub/incoming/kerins/vlm/
\\
  Hubble Space Telescope (HST) limits on the amount of halo dark matter (DM) in
the form of very low-mass (VLM) stars close to the hydrogen-burning limit have
been interpreted as excluding such stars as viable candidates. However, these
limits assume that the stars are smoothly distributed and have at least the
metallicity of Population II stars, whilst some baryonic DM formation theories
predict that they may instead be clumped into globular-cluster configurations
and have close to zero metallicity. I re-analyse the HST data employing the
zero-metallicity VLM star models of Saumon et al. (1994), which predict V-I
colours below the cuts of previous analyses. From the models I derive new
limits on the allowed halo fraction comprising VLM stars for both the
unclustered and clustered cases. In the unclustered regime I find a 95% upper
limit on the allowed halo fraction of 1.4% inferred from 20 HST fields,
comparable to limits derived by previous studies for non-zero metallicity
populations. In the cluster scenario I show that clusters of mass M and radius
R can satisfy both HST and the recent MACHO gravitational microlensing results,
which indicate a lens halo fraction of 40% for a standard halo model, provided
$R < 1.2 (M/10^4 Mo)^0.74 pc$. However, existing dynamical limits restrict the
allowed range to a tiny region characterised by $M \sim 4x10^4$ Mo and R$ \sim 3
pc$. Furthermore, consistency between MACHO and HST demands a present-day
clustering efficiency of 92% or better. Intriguingly however, the cluster mass
implied by these limits is theoretically well motivated and the VLM star
scenario may also help to provide an explanation for the faint red `halo' light
recently reported around another galaxy.
 (http://xxx.lanl.gov/abs/astro-ph/9610070 ,  54kb)
\\


Paper: astro-ph/9611217
From: C. R. Keeton ckeeton@mars.harvard.edu
Date: Tue, 26 Nov 1996 10:47:59 MST

Title: Gravitational Lensing Limits on Early-Type Galaxies
Authors: C.S. Kochanek and C.R. Keeton (Harvard-Smithsonian Center for
  Astrophysics)
Comments: 10 pages, 6 figures Proc. of the Second Stromlo Symposium, The Nature
  of Elliptical Galaxies
\\
  Gravitational lenses are a unique new constraint on the structure of
galaxies. We review the evidence that most lenses are early-type galaxies, the
optical properties of the lens galaxies, the evidence against constant M/L
models, recent work on the axis ratios of the mass distribution, and the role
stellar dynamics plays in gravitational lensing.
 (http://xxx.lanl.gov/abs/astro-ph/9611217 ,  206kb)
\\


Paper: astro-ph/9608138
From: mhlee@lola.phy.queensu.ca (Man Hoi Lee)
Date: Thu, 22 Aug 1996 01:17:57 -0400

Title: Statistics of Gravitational Microlensing Magnification. I.
  Two-Dimensional Lens Distribution
Authors: Lev Kofman, Nick Kaiser, Man Hoi Lee, and Arif Babul
Comments: 35 pages, including 6 figures; uses AASTeX v4.0 macros; submitted to
  ApJ
Report-no: UH IfA-96-46
\\
  (Abridged) In this paper we refine the theory of microlensing for a planar
distribution of point masses. We derive the macroimage magnification
distribution P(A) at high magnification (A-1 >> $tau^2$) for a low optical depth
(tau << 1) lens distribution by modeling the illumination pattern as a
superposition of the patterns due to individual ``point mass plus weak shear''
lenses. We show that a point mass plus weak shear lens produces an astroid-
shaped caustic and that the magnification cross-section obeys a simple scaling
property. By convolving this cross-section with the shear distribution, we
obtain a caustic-induced feature in P(A) which also exhibits a simple scaling
property. This feature results in a 20% enhancement in P(A) at A approx 2/tau.
In the low magnification (A-1 << 1) limit, the macroimage consists of a bright
primary image and a large number of faint secondary images formed close to each
of the point masses. Taking into account the correlations between the primary
and secondary images, we derive P(A) for low A. The low-A distribution has a
peak of amplitude ~ $1/tau^2$ at A-1 ~ $tau^2$ and matches smoothly to the high-A
distribution. We combine the high- and low-A results and obtain a practical
semi-analytic expression for P(A). This semi-analytic distribution is in
qualitative agreement with previous numerical results, but the latter show
stronger caustic-induced features at moderate A for tau as small as 0.1. We
resolve this discrepancy by re-examining the criterion for low optical depth. A
simple argument shows that the fraction of caustics of individual lenses that
merge with those of their neighbors is approx 1-exp(-8 tau). For tau=0.1, the
fraction is surprisingly high: approx 55%. For the purpose of computing P(A) in
the manner we did, low optical depth corresponds to tau << 1/8.
 (http://xxx.lanl.gov/abs/astro-ph/9608138 ,  131kb)
\\


Paper: astro-ph/9610162
From: wes@astro.Princeton.EDU
Date: Mon, 21 Oct 1996 14:05:56 -0400 (EDT)

Title: A Robust Determination of the Time Delay in 0957+561A,B and a
  Measurement of the Global Value of Hubble's Constant
Authors: Tomislav Kundic (Th. Astroph., Caltech), Edwin L. Turner, Wesley N.
  Colley, J. Richard Gott, III, James E. Rhoads, Yun Wang (Princeton), Louis E.
  Bergeron, Karen A. Gloria, Daniel C. Long (Apache Point Observ.), Sangeeta
  Malhotra (IPAC), Joachim Wambsganss (Astroph. Inst., Potsdam)
Comments: AASTeX 4.0
Report-no: Princeton Observatory Preprint 687
\\
  Photometric monitoring of the gravitational lens system 0957+561A,B in the g
and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996
shows a sharp g band event in the trailing (B) image light curve at the precise
time predicted from the observation of an event during 1995 in the leading (A)
image with a delay of 415 days. This success confirms the "short delay," and
the lack of any feature at a delay near 540 days rejects the "long delay" for
this system, resolving a long-standing controversy. A series of statistical
analyses of our light curve data yield a best fit delay of 417 +/- 3 days (95%
confidence interval). Recent improvements in the modeling of the lens system
(consisting of a galaxy and cluster) allow us to derive a value of the global
(at z = 0.36) value of Hubble's constant $H_0$ using Refsdal's method, a simple
and direct distance determination based on securely understood physics and
geometry. The result is $H_0 = 63 +/- 12 km/s/Mpc$ (for Omega = 1) where this 95%
confidence interval is dominated by remaining lens model uncertainties.
 (http://xxx.lanl.gov/abs/astro-ph/9610162 ,  172kb)
Paper: astro-ph/9610162
replaced with revised version Wed, 8 Jan 1997 14:49:13 -0500 (EST)

Title: A Robust Determination of the Time Delay in 0957+561A,B and a
  Measurement of the Global Value of Hubble's Constant
Authors: Tomislav Kundic (Th. Astroph., Caltech), Edwin L. Turner, Wesley N.
  Colley, J. Richard Gott, III, James E. Rhoads, Yun Wang (Princeton), Louis E.
  Bergeron, Karen A. Gloria, Daniel C. Long (Apache Point Observ.), Sangeeta
  Malhotra (IPAC), Joachim Wambsganss (Astroph. Inst., Potsdam)
Comments: accepted by ApJ, AASTeX 4.0 preprint, 4 PostScript figures
Report-no: Princeton Observatory Preprint 687
 
(http://xxx.lanl.gov/abs/astro-ph/9610162 ,  173kb)
\\


Paper: astro-ph/9608139
From: mhlee@lola.phy.queensu.ca (Man Hoi Lee)
Date: Thu, 22 Aug 1996 01:19:57 -0400

Title: Statistics of Gravitational Microlensing Magnification. II.
  Three-Dimensional Lens Distribution
Authors: Man Hoi Lee, Arif Babul, Lev Kofman, and Nick Kaiser
Comments: 52 pages, including 15 figures (Figures 3, 6, and 10 have been
  bitmapped); uses AASTeX v4.0 macros; submitted to ApJ
Report-no: UH IfA-96-47
\\
  In Paper I we studied the theory of gravitational microlensing for a planar
distribution of point masses. In this second paper, we extend the analysis to a
three-dimensional lens distribution. First we study the lensing properties of
three-dimensional lens distributions by considering in detail the critical
curves, the caustics, the illumination patterns, and the magnification
cross-sections sigma(A) of multiplane configurations with two, three, and four
point masses. For $N_\ast$ point masses that are widely separated in Lagrangian
space, we find that there are $~ 2^{N_\ast} - 1$ critical curves in total, but
that only $~ N_\ast$ of these produce prominent caustic-induced features at the
high magnification end of sigma(A).
  In the case of a low optical depth random distribution of point masses, we
show that the multiplane lens equation near a point mass can be reduced to the
single plane equation of a point mass perturbed by weak shear. This allows us
to calculate the caustic-induced feature in the macroimage magnification
distribution P(A) as a weighted sum of the semi-analytic feature derived in
Paper I for a planar lens distribution. The resulting semi-analytic
caustic-induced feature is similar to the feature in the planar case, but it
does not have any simple scaling properties, and it is shifted to higher
magnification. The semi-analytic distribution is compared to the results of
previous numerical simulations for optical depth tau ~ 0.1, and they are in
better agreement than a similar comparison in the planar case. We explain this
by estimating the fraction of caustics of individual lenses that merge with
those of their neighbors. For tau=0.1, the fraction is approx 20%, much less
than the approx 55% for the planar case.
 (http://xxx.lanl.gov/abs/astro-ph/9608139 ,  436kb)
\\


Paper: astro-ph/9702191
From: jlehar@astrometry.harvard.edu (Joseph Lehar)
Date: Fri, 21 Feb 1997 12:05:23 -0500   (83kb)

Title: The Gravitationally-Lensed Radio Source MG0751+2716
Authors: J. Lehar (1), B.F. Burke (2), S.R. Conner (2), E.E. Falco (1), A.B.
  Fletcher (2), M. Irwin (4), R.G. McMahon (5), T.W.B. Muxlow (3), P.L.
  Schechter (2) ((1)CfA, (2)MIT, (3)NRAL, (4)RGO, (5)IoA)
Comments: 1 Latex aaspp4 manuscript, 17 pages with 5 postscript figures.
  Submitted to AJ 1997.02.19
\\
  We report the discovery of a new gravitationally lensed radio source. Radio
maps of MG0751+2716 show four lensed images, which, at higher resolution, are
resolved into long arcs of emission. A group of galaxies is present in optical
images, including the principal lensing galaxy, with a much brighter galaxy
just a few arcseconds away. We have measured the redshift of this brighter
galaxy. Lens models that can readily reproduce the lensed image positions all
require a substantial shear component. However, neither the very elongated lens
nor the bright nearby galaxy are correctly positioned to explain the shear.
Lens models which associate the mass with the light of galaxies in the group
can produce an acceptable fit, but only with an extreme mass-to-light ratio in
one of the minor group members.
 ( http://xxx.lanl.gov/abs/astro-ph/9702191 ,  83kb)
\\


Paper: astro-ph/9606141
From: e.linder@ic.ac.uk
Date: Fri, 21 Jun 1996 16:01:54 +0100

Title: CORRELATED GRAVITATIONAL LENSING OF THE CMB
Author: Eric V. Linder (Imperial College London)
Comments: uuencoded gzipped tarred TeX and PostScript files, 13 pages, 1 figure
Report-no: Imperial/Astro/96-8
\\
  Cosmological inhomogeneities gravitationally deflect radiation propagating
from distant sources, transforming the spatial and angular correlation
functions of intrinsic source properties. For a gaussian distribution of
deflections (e.g. from a primordial gaussian density perturbation spectrum or
from the central limit theorem) we calculate the probability distributions for
geodesic deviations. If the intrinsic variable is also gaussian, e.g. the large
scale velocity flow field or cosmic microwave background temperature
anisotropies, then distributions and correlation functions of the observed
image sky properties can be obtained. Specialising to CMB temperature
fluctuations we rederive simply the influence of independent gravitational
lensing on the anisotropy angular correlation function and calculate the new
effect of lensing correlated with the anisotropies, e.g. arising from the same
primordial gravitational perturbation field. Characteristic magnitudes and
scales are given in terms of the density power spectrum. The correlated
deflection-temperature effect is shown to be negligible.
(http://xxx.lanl.gov/abs/astro-ph/9606141 ,  15kb)
\\


Paper: astro-ph/9702042
From: Charley Lineweaver charley@cdsxb6.u-strasbg.fr
Date: Tue, 4 Feb 1997 22:26:48 +0100   (182kb)

Title: Gold in the Doppler Hills: Cosmological Parameters in the Microwave
  Background
Authors: C. H. Lineweaver (Observatoire de Strasbourg)
Comments: 21 pages, 11 figures, to appear in the Proceedings of the
  International School in Astrophysics: "From Quantum Fluctuations to
  Cosmological Structures" held in Casablanca, Morocco, December 1 - 10, 1996
\\
  Research on the cosmic microwave background (CMB) is progressing rapidly. New
experimental groups are popping up and two new satellites will be launched. The
current enthusiasm to measure fluctuations in the CMB power spectrum at angular
scales between 0.1 and 1 degree is largely motivated by the expectation that
CMB determinations of cosmological parameters will be of unprecedented
precision: cosmological gold. In this article I will try to answer the
following questions: 1) What is the CMB? 2) What are cosmological parameters?
3) What is the CMB power spectrum? 4) What are all those bumps in the power
spectrum? 5) What are the current CMB constraints on cosmological parameters?
 ( http://xxx.lanl.gov/abs/astro-ph/9702042 ,  182kb)
\\


Paper: astro-ph/9701100
From: Avi Loeb loeb@cfata1.harvard.edu
Date: Wed, 15 Jan 1997 17:15:09 -0500

Title: Gravitational Lensing of Quasars by Spiral Galaxies
Author: Abraham Loeb  (Harvard Univ)
Comments: 4 pages, 2 figures, contribution to Texas symposium 1996
\\
  Gravitational lensing by a spiral galaxy occurs when the line-of-sight to a
background quasar passes within a few kpc from the center of the galactic disk.
Since galactic disks are rich in neutral hydrogen, the quasar spectrum will
likely be marked by a damped Lyman-alpha absorption trough at the lens
redshift. Therefore, the efficiency of searches for gravitational lensing with
sub-arcsecond splitting can be enhanced by 1-2 orders of magnitude by focusing
on a subset of all bright quasars which show low-redshift (z<1) strong
Lyman-alpha absorption $(N>10^{21} cm^{-2})$. The double-image signature of
lensing could, in principle, be identified spectroscopically and without the
need for high-resolution imaging. The absorption spectrum of a spiral lens
would show a generic double-step profile due to the superposition of the two
absorption troughs of the different images. Finally, we note that searches for
microlensing signatures of quasars with damped Lyman-alpha absorption could
calibrate the fraction of MACHOs in galactic halos at high redshift.
 (http://xxx.lanl.gov/abs/astro-ph/9701100 ,  25kb)
\\


Paper: astro-ph/9610222
From: pyl@gag.observ-gr.fr (Pierre-Yves Longaretti)
Date: Mon, 28 Oct 1996 12:36:13 +0100

Title: Lens reconstruction and source redshift distribution
Author: Pierre-Yves Longaretti (Observatoire de Grenoble, France)
Comments: 4 pages, LaTex, Springer-Verlag's LaTeX Astronomy and Astrophysics
  macro package, submitted to A and A Letters
\\
  The currently used linear and nonlinear lens inversion techniques are based
on distortion estimators whose complicated source redshift dependence makes the
influence of the redshift distribution of the sources difficult to take into
account and to analyze. However, the lens equations can be explicitly averaged
over the source redshift distribution by a suitable choice of the estimators.
Lens reconstruction procedures are outlined, which make use of all the
information and in which all the unknown quantities of the problem can be
recovered simultaneously in both the linear and nonlinear regime, for either
noncritical or critical lenses. These procedures require no prior knowledge of
the redshift distribution of the sources, but are possibly dependent on the
Cosmology in some instances. Possible methods of recovery of the source
redshift distribution itself are briefly discussed at the same time.
 (http://xxx.lanl.gov/abs/astro-ph/9610222 ,  8kb)
\\


Paper: astro-ph/9610233
From: Sangeeta Malhotra san@ipac.caltech.edu
Date: Mon, 28 Oct 1996 21:24:04 MST

Title: Through a Lens Darkly: Evidence for Dusty Gravitational Lenses
Authors: Sangeeta Malhotra (IPAC), James E. Rhoads (KPNO), Edwin L. Turner
  (Princeton)
Comments: Sumitted to MNRAS, 6 pages, 3 figures. Also available at
  http://www.astro.princeton.edu/~san/Abstracts/dusty.html
\\
  Foreground galaxies that amplify the light from background quasars may also
dim that light if the galaxies contain enough dust. Extinction by dust in
lenses could hide the large number of lensed systems predicted for a flat
universe with a large value of the cosmological constant $\Lambda$. We look for
one signature of dust, namely reddening, by examining optical-infrared colors
of gravitationally lensed images of quasars. We find that the lensed systems
identified in radio and infrared searches have redder optical-IR colors than
optically selected ones. This could be due to a bias against selecting reddened
(hence extincted) quasars in the optical surveys, or due to the differences in
the intrinsic colors of optical and radio quasars. Comparison of the
radio-selected lensed and unlensed quasars shows that the lensed ones have
redder colors. We therefore conclude that at least part of the color difference
between the two lens samples is due to dust.
  From the color difference between lensed and unlensed radio quasars (and
assuming Galactic extinction law) we can reconcile a large cosmological
constant ($\Lambda=0.9$) with the number of lensed systems observed in flux
limited optical surveys. These results substantially weaken the strongest
constraint on cosmological scenarios that invoke a non-zero cosmological
constant to explain age discrepancy problems, satisfy predictions of
inflationary models of the early universe and play a role in large scale
structure formation models. They also raise the prospect of using gravitational
lenses to study the interstellar medium in high redshift galaxies.
 (http://xxx.lanl.gov/abs/astro-ph/9610233 ,  23kb)
\\


Paper: astro-ph/9701110
From: Ariyeh Maller <maller@maxwell.UCSC.EDU>
Date: Thu, 16 Jan 1997 13:17:59 -0800

Title: Inclination Effects in Spiral Galaxy Gravitational Lensing
Authors: Ariyeh Maller, Ricardo Flores, Joel Primack
Comments: 10 pages, AAS LaTex, 5 postscript figures
\\
  Spheroidal components of spiral galaxies have been considered the only
dynamically important component in gravitational lensing studies thus far. Here
we point out that including the disk component can have a significant effect,
depending on the disk inclination, on a variety of lensing properties that are
relevant to present studies and future surveys. As an example, we look at the
multiple image system B1600+434, recently identified as being lensed by a
spiral galaxy. We find that including the disk component one can understand the
fairly large image separation as being due to the inclination of a typical
spiral, rather than the presence of a very massive halo. The fairly low
magnification ratio can also be readily understood if the disk is included. We
also discuss how such lensed systems might allow one to constrain parameters of
spiral galaxies such as a disk-to-halo mass ratio, and disk mass scale
length. Another example we consider is the quasar multiple-lensing cross
section, which we find can increase many-fold at high inclination for a
typical spiral. Finally, we discuss the changes in the gravitational lensing
effects on damped Lyman alpha systems (DLAS) when disk lensing is included.
 (http://xxx.lanl.gov/abs/astro-ph/9701110 ,  78kb)
\\


Paper: astro-ph/9612159
From: Dan Maoz <dani@wise1.tau.ac.il>
Date: Tue, 17 Dec 1996 12:43:51 +0200

Title: A survey for large image-separation lensed quasars
Authors: Dan Maoz, Hans-Walter Rix, Avishay Gal-Yam, and Andrew Gould
Comments: LaTex, ApJ, submitted
\\
  The statistics of gravitationally lensed quasars with multiple images in the
0.1''-7'' range have been measured in various surveys. Little is known,
however, about lensed-quasar statistics at larger image separations, which
probe masses on the scale of galaxy clusters. We extend the results of the HST
Snapshot Survey for Lensed Quasars to the 7''-50'' range for a sub-sample of 76
quasars that is free of known selection effects. Using a combination of
multicolor photometry and spectroscopy, we show that none of the point sources
in the entire field of view of the HST observations of these quasars are lensed
images. Large-separation quasar lensing is therefore not common. We carry out a
detailed calculation of the expected statistics of large-separation lensing for
this quasar sample, incorporating realistic input for the mass profiles and
mass function of galaxy clusters. We find that the observational null results
are consistent with the expected effect of galaxy clusters, even if these have
existed in their present form and number since z of about 2. The rarity of
large-separation lensed quasars can rule out some extreme scenarios, e.g. that
the mass-function of clusters has been severely underestimated, or that large
mass concentrations that are not associated with galaxies (i.e. ``failed''
clusters) are common. The rareness of wide lensing also sets limits on the
cosmological constant that are independent of limits derived from galaxy
lensing. The lensing statistics of larger quasar samples can probe the
structure, number, and evolution of clusters, as well as the geometry of space.
 (http://xxx.lanl.gov/abs/astro-ph/9612159 ,  75kb)
\\


Paper: astro-ph/9609187
From: draza <draza@tac.dk>
Date: Thu, 26 Sep 1996 15:27:27 MDT

Title: Microlensing, structure of the galactic halo and determination of dark
  objects' mass function
Authors: D. Markovic and J. Sommer-Larsen (Theoretical Astrophysics Center,
  Copenhagen)
Comments: MNRAS LaTeX style, 14 pages, 11 figures embedded
\\
  We study the accuracy of inference of the massive halo objects' (MHO or
`Macho') mass function from microlensing events observed toward LMC. Assuming
the spatial distribution and kinematics of the objects are known, the slope and
the range of the MHO mass function (modeled here by a simple power law) will be
possible to determine from 100-1000 detected events if the slope $\alpha$ is in
the range [-2.5, -0.5], with the statistical errors reaching their minima at
$\alpha =-1.5$. Outside this range the errors grow rapidly making the inference
difficult even at very large numbers of events ($N\simeq 10000$). On the other
hand, the average mass of the MHOs will be determined to better than about 30%
accuracy from $N\simeq 100$ events for any slope. We find that the accuracy of
inference at fixed N will not be strongly affected by the presently available
detection efficiencies if the typical MHO masses are in the range indicated by
the events detected so far.
  We also estimate the effects of uncertainty of the MHOs' spatial distribution
and kinematics on the determination of their mass function. The halo models
considered are all spherical but we allow for various density profiles and a
radius-dependent, anisotropic velocity dispersion. We find that, while the mass
function slope and range are weakly affected for $-2.5 < \alpha < 0$, the error
in the average mass due to the halo uncertainties could be reduced to less than
50\% only through the detection of 1000 or more events. Reliable estimates of
the halo structure itself [density profile and velocity dispersion profile] can
start only at very large numbers of detections, N > 10000.
 (http://xxx.lanl.gov/abs/astro-ph/9609187 ,  222kb)

Paper: astro-ph/9609187
replaced with revised version Thu, 12 Dec 1996 20:00:55 MST

Title: Microlensing, structure of the galactic halo and determination of dark
  objects' mass function
Authors: D. Markovic and J. Sommer-Larsen (Theoretical Astrophysics Center,
  Copenhagen)
Comments: MNRAS LaTeX style, 14 pages, 11 figures embedded; some changes in the
  estimates of the last section; a few references added. Also available from
  http://www.tac.dk/~draza/papers/macho1.ps.Z
Report-no: 1996-024
 (http://xxx.lanl.gov/abs/astro-ph/9609187 ,  201kb)
\\


Paper: astro-ph/9702231
From: martinez@astax1.ifca.unican.es
Date: Wed, 26 Feb 1997 19:51:30 +0100   (60kb)

Title: The Effect of Weak Gravitational Lensing on the Cosmic Microwave
  Background Anisotropy: Flat versus Open Universes
Author: Enrique Martinez-Gonzalez, Jose L. Sanz and Laura Cayon
Comments: latex file in ApJ style, 17 pages, 3 ps figures
Report-no: IFCA-26
\\
  We have studied the effect of gravitational lensing on the Cosmic Microwave
Background (CMB) anisotropy in flat and open universes. We develop a formalism
to calculate the changes on the radiation power spectrum induced by lensing in
the Newtonian and synchronous-comoving gauges. The previously considered
negligible contribution to the CMB radiation power spectrum of the anisotropic
term of the lensing correlation is shown to be appreciable. However,
considering the nonlinear evolution of the matter power spectrum produces only
slight differences on the results based on linear evolution. The general
conclusion for flat as well as open universes is that lensing slightly smoothes
the radiation power spectrum. For a given range of multipoles the effect of
lensing increases with Omega but for the same acoustic peak it decreases with
$\Omega$. The maximum contribution of lensing to the radiation power spectrum
for $l\leq 2000$ is $\sim$ 5% for $\Omega$ values in the range 0.1-1.
 ( http://xxx.lanl.gov/abs/astro-ph/9702231 ,  60kb)
\\


Paper: astro-ph/9601145
From: MASSO@IFAE.ES
Date: Thu, 25 Jan 1996 14:05:05 GMT+0100

Title: BARYONIC DARK MATTER: THEORY AND EXPERIMENT. OVERVIEW
Authors: Eduard Masso (IFAE and Dep. Fisica, Univ. Autonoma de Barcelona)
Comments: Written version of a talk at IV Workshop on Theoretical and
  Phenomenological Aspects of Underground Physics, TAUP95, Toledo (Spain),
  Sept. 17-21
Report-no: UAB-FT-380
\\
  The general arguments for baryonic and galactic dark matter are presented.
Limits coming from a variety of theoretical considerations and observations are
discussed. The surviving candidates for galactic baryonic dark matter seem most
likely to be in the form of compact objects and could be in one of two mass
windows: either in the brown dwarf regime or in the mass range corresponding to
supermassive black holes. Microlensing towards LMC is probing the first window.
It is important to keep in mind that these experiments may detect compact heavy
objects, independent of their constituency.
(http://xxx.lanl.gov/abs/astro-ph/9601145 ,  14kb)
\\


Paper: astro-ph/9703015
From: Smita Mathur <smita@head-cfa.harvard.edu>
Date: Mon, 03 Mar 1997 14:06:54 -0500   (16kb)

Title: X-ray Absorption Towards The Einstein Ring Source PKS1830-211
Authors: Smita Mathur (Harvard-Smithsonian Center for Astrophysics) and Sunita
  Nair (Univ. of Manchester)
Comments: To appear in the ApJ Vol. 484, July 20, 1997. LaTex, 15 pages.
  Requires AAS macros
\\
  PKS1830-211 is an unusually radio-loud gravitationally lensed quasar. In
the radio, the system appears as two compact, dominant features surrounded by
relatively extended radio emission which forms an Einstein Ring. As the line of
sight to it passes close to our Galactic center, PKS1830-211 has not been
detected in wave-bands other than the radio and X-ray so far. Here we present
X-ray data of PKS1830-211 observed with ROSAT PSPC. The X-ray spectrum shows
that absorption in excess of the Galactic contribution is highly likely, which
at the redshift of the lensing galaxy ($z_l=0.886$) corresponds to
N$_H=3.5^{+0.6}_{-0.5}\times 10^{22}$ atoms cm$^{-2}$. The effective optical
extinction is large, A$_V$(observed)$gax 5.8$. When corrected for this 
additional
extinction, the two point optical to X-ray slope $aox$ of PKS1830-211 lies just
within the observed range of quasars. It is argued here that both compact
images must be covered by the X-ray absorber(s) which we infer to be the
lensing galaxy(galaxies). The dust to gas ratio along the line of sight within
the lensing galaxy is likely to be somewhat larger than for our Galaxy.
 ( http://xxx.lanl.gov/abs/astro-ph/9703015 ,  16kb)
\\


Paper: astro-ph/9608105
From: mellier@iap.fr (Yannick Mellier)
Date: Fri, 16 Aug 96 08:15:31 +0200

Title: Weak lensing at the limit of the sky background noise
Authors: Y. Mellier (1,2), B. Fort (2) ((1) Institut d'Astrophysique de Paris,
  (2) Observatoire de Paris DEMIRM)
Comments: 12 pages, Contributed talks for the ESO Workshop on "The Early 
  Universe with the VLT" 1-4 April 1996. Latex with lamuphys.sty and
  psfig.sty, Latex, 12 pages, 6 figures, also available on
  ftp.iap.fr/pub/incoming/mellier.
\\
Recent weak lensing observations have pushed the use of 4 meter-class
telescopes to the limits of their capabilities with exposure times exceeding
several hours.  The leading idea is that the surface density of faint
galaxies up to very faint magnitude ($B > 28-30$) raises continuously thus
potentially offering a dense template of distant sources whose intensity
contrast is at the sky noise level.  In complement to the Peter Schneider's
presentation on dark matter search from weak lensing (this conference), we
review some of these recent advances in weak lensing analysis based on this
extreme faint population of galaxies in order to explore:
  the dark matter distribution on large scales,
  the redshift ditribution of lensed sources at very large distance,
  and eventually the values of cosmological parameters.
For each observational topic we will briefly discuss these new methods as
compare to more classical lensing studies as well as the possible VLT
scientific impact in the domain.
 (http://xxx.lanl.gov/abs/astro-ph/9608105 ,  185kb)
\\


Paper: astro-ph/9608158
From: mellier@iap.fr (Yannick Mellier)
Date: Sun, 25 Aug 96 09:01:33 +0200

Title: Gravitational Lensing and the Redshift Distribution of $B>25$ galaxies
Authors: Y. Mellier (1,2) ((1) Institut d'Astrophysique de Paris, (2)
  Observatoire de Paris DEMIRM)
Comments: 8 pages, Invited talks for the 37th Herstmonceux Conference on "HST
  and the High Redshift Universe" 1-5 july 1996. Latex with hx37\_latex.sty and
  psfig.sty. 8 pages, 4 figures 191K gzipped tar file. Also available on
  ftp.iap.fr/pub/incoming/mellier
\\
  In addition to the determination of the mass distribution of lenses (see P.
Schneider, this conference), strong and weak lensing can also be powerfull
tools to analyse the redshift distribution of faint galaxies. In this review, I
summarize the present status of redshifts of galaxies beyond $B=25$ as they are
inferred by spectroscopy of magnified galaxies, lensing inversion and
magnification bias.
 (http://xxx.lanl.gov/abs/astro-ph/9608158 ,  176kb)
\\


Paper: astro-ph/9609197
From: fbernard@wasa.saclay.cea.fr (Francis Bernardeau)
Date: Mon, 30 Sep 1996 12:11:54 +0200

Title: Recent Advances in Gravitational Lensing
Authors: Y. Mellier (Obs. Paris and IAP), L. van Waerbeke (Obs. Midi-Pyrenees),
  F. Bernardeau (SPhT Saclay) and B. Fort (Obs. Paris)
Comments: Invited talk for the VIIIth Rencontres de Blois, "Neutrinos, Dark
  Matter and the Universe" 6-12 june 1996. Latex, 15 pages, 6 figures. Also
  available on ftp://ftp.iap.fr/pub/incoming/mellier
Report-no: Saclay SPhT T96/109
\\
  The gravitational lensing effect is one of the most promising tools for
cosmology. Indeed it probes directly the total mass distribution in large-scale
structures and can as well provide valuable informations on the values of the
density parameter Omega and the cosmological constant lambda. In this review we
summarize the most spectacular observational and theoretical advances obtained
in this field during the last five years.
 (http://xxx.lanl.gov/abs/astro-ph/9609197 ,  607kb)
\\


Paper: astro-ph/9505100
From: mohanty@prl.ernet.in (SUBHENDRA MOHANTY )
Date: Mon, 22 May 1995 13:37:39 +0530

Title: NO BIREFRINGENCE IN EINSTEIN'S GRAVITY
Authors: S. Mohanty and A.R. Prasanna
Comments: latex file no figures
\\
  Einstein's theory predicts that, massive test particles with non-zero spin or
angular momentum, in an external gravitation field, follow geodesics which
depend upon the orientation of the spin-angular momentum . It has been claimed
that such an effect also holds for photons i.e. photons with different
helicities follow different geodesics in the gravitational field of a rotating
body and would give rise to a polarisation dependent deflection of light
passing in the vicinity of the sun or a polarisation dependent time delay of
pulsar signals . We show here that contrary to earlier claims , in Einstein's
gravity there is no birefringence and photons follow null geodesics
irrespective of polarisation. Thus if gravitational birefringence is ever
observed experimentally it would be a signal of new physics beyond Einstein's
gravity
\\


Paper: astro-ph/9612074
From: Nakamura Takahiro (UTAP) 

nakamura@utaphp1.phys.s.u-tokyo.ac.jp
Date: Sat, 07 Dec 1996 20:00:34 +0900

Title: Strong Gravitational Lensing and Velocity Function as Tools to Probe
  Cosmological Parameters: Current Constraints and Future Predictions
Authors: Takahiro T. Nakamura and Yasushi Suto (University of Tokyo)
Comments: 27 pages, 8 figures, ptptex. Progress of Theoretical Physics, in
  press
Report-no: UTAP-236/96, RESCEU-23/96
\\
  Constraints on cosmological models from strong gravitational lensing
statistics are investigated. We pay particular attention to the role of the
velocity function in the calculation of the lensing probability. The velocity
function derived from the observed galaxy luminosity function, which is used in
most previous work, is unable to predict the large separation lensing events.
In this paper, we also use the Press-Schechter theory to construct a velocity
function theoretically. Model predictions are compared with the observed
velocity function and the HST snapshot survey. Comparison with the latter
observation shows that the predictions based on the theoretical velocity
function are consistent with the observed large separation events in COBE
normalized low-density models, especially with a non-vanishing cosmological
constant. Adopting the COBE normalization, however, we could find no model
which simultaneously satisfies both the observed velocity function and the HST
snapshot survey. We systematically investigate various uncertainties in the
gravitational lensing statistics including finite core radius, the distance
formula, magnification bias, and dust obscuration. The results are very
sensitive to these effects as well as theoretical models for the velocity
function, implying that current limits on the cosmological parameters should be
interpreted with caution. Predictions for future surveys are also presented.
 (http://xxx.lanl.gov/abs/astro-ph/9612074 ,  180kb)
\\


Paper: astro-ph/9606001
From: Matthias Bartelmann 

msb@MPA-Garching.MPG.DE
Date: Mon, 3 Jun 1996 08:45:37 +0200 (MDT)

Title: LECTURES ON GRAVITATIONAL LENSING
Authors: Ramesh Narayan (1) and Matthias Bartelmann (2) ((1)
  Harvard-Smithsonian Center for Astrophysics; (2) Max-Planck-Institut fuer
  Astrophysik)
Comments: Lectures held at the 1995 Jerusalem Winter School; 51 pages without
  figures; postscript file including figures can be retrieved from
  
http://www.mpa-garching.mpg.de/Lenses/Preprints/JeruLect.ps.gz
\\
  The Lectures give an introduction to Gravitational Lensing. We discuss
lensing by point masses, lensing by galaxies, and lensing by clusters and
larger-scale structures in the Universe. The relevant theory is developed and
applications to astrophysical problems are discussed.
(http://xxx.lanl.gov/abs/astro-ph/9606001 ,  61kb)
\\


Paper: astro-ph/9509016
From: Preprint account preprint@ast.cam.ac.uk
Date: Mon, 4 Sep 1995 17:51:00 +0100 (BST)

Title: STUDY OF THE DYNAMICS OF THE CORE OF A2218
Author: Priyamvada Natarajan
Comments: uuencoded compressed postscript, without figure. The preprint is
  available in complete form at 
\\
http://www.ast.cam.ac.uk/preprint/PrePrint.html
Report-no: CAP-9509005
\\
  We report the results of an attempt to study the velocity structure of the
core of the cluster A2218 in order to probe its dynamical state. The aim is to
understand if the core is indeed virialized? relaxed? or in hydrodynamic
equilibrium? We use cluster lensing data in conjunction with the optical galaxy
data to solve in detail for the nature of galaxy orbits and the velocity
anisotropy in the core. We present our preliminary results below.
\\


Paper: astro-ph/9509029
From: Preprint account preprint@ast.cam.ac.uk
Date: Wed, 6 Sep 1995 15:18:31 +0100 (BST)

Title: EFFECT OF SUB-STRUCTURE IN CLUSTERS ON THE LOCAL WEAK-SHEAR FIELD
Author: Priyamvada Natarajan and Jean-Paul Kneib
Comments: uuencoded compressed postscript. The preprint is also available at
\\
 http://www.ast.cam.ac.uk/preprint/PrePrint.html
Report-no: CAP-9509007
\\
  Weak shear maps of the outer regions of clusters have been successfully used
to map the distribution of mass at large radii. The effects of substructure in
clusters on such reconstructions of the total mass have not been systematically
studied. We propose a new method to study the effect of perturbers (bright
cluster galaxies or sub-groups within the cluster) on the weak shear field. We
present some analytic results below.
\\


Paper: astro-ph/9604084
replaced with revised version Mon, 30 Sep 1996 09:18:13 +0100 (BST)

Title: An analytic approximation to the isothermal sphere
Author: Priyamvada Natarajan (IoA, Cambridge) and Donald Lynden-Bell (IoA,
  Cambridge and University, Belfast)
Comments: 6 pages, figures included, revised version, accepted for publication
  in MNRAS
Report-no: CAP-9604002
 (http://xxx.lanl.gov/abs/astro-ph/9604084 ,  115kb)
\\


Paper: astro-ph/9607063
From: Doris Neumann 

don@rosat.mpe-garching.mpg.de
Date: Fri, 12 Jul 1996 11:43:03 +0200 (MET DST)

Title: X-RAY PROPERTIES OF THE DISTANT CLUSTER Cl0016+16
Authors: Doris M. Neumann, Hans Boehringer (MPE)
Comments: 11 pages, submitted to MNRAS
Report-no: MPE Preprint 369
\\
  We present X-ray data on the distant cluster Cl0016+16 (z=0.5545) from ROSAT
PSPC and HRI observations and use them to study the physics of the intracluster
medium (ICM) and the dynamical state of the cluster. The surface brightness
distribution is not only described by a spherically symmetric model but also by
a two-dimensional $\beta $-model fit. Subtracting an elliptical model cluster
as defined by the best fit parameters of the two-dimensional model we find
significant residuals, indicating an additional, extended X-ray source within
the cluster. This source, likely to be a merging subcomponent of the cluster,
coincides with a peak in the weak lensing mass map of Smail et. al. (1995). In
the course of this analysis we present a new approach to quantify the
significance of substructure in cluster X-ray images dominated by Poisson noise
and smoothed with a Gauss filter. We determine the radial mass profile
integrated out to a radius of 3Mpc and find for the total mass of the cluster a
value of $\sim 1.4-3.3 \times 10^{15} M_{odot}$ and $\sim 4.5 \times 10^{14} 
M_{odot}$ for the gas mass, yielding a gas-to-total mass ratio of 14-32\%. There is
no significant radial dependence of the gas-to-total mass ratio in the cluster.
 (http://xxx.lanl.gov/abs/astro-ph/9607063 ,  135kb)
\\


Paper: astro-ph/9701060
From: nikolaev@kestrel.phast.umass.edu (Sergei Nikolaev)
Date: Mon, 13 Jan 1997 11:38:03 -0500 (EST)

Title: A rigorous reanalysis of the IRAS variable population: scale lenghts,
  asymmetries, and microlensing
Authors: Sergei Nikolaev and Martin D. Weinberg
Comments: 22 pages, LaTeX, 12 figures
\\
  Previous work reported a bar signature in color-selected IRAS variable stars.
Here, we estimate the source density of these variables while consistently
accounting for spatial incompleteness in data using a likelihood approach. The
existence of the bar is confirmed with shoulder of 4 kpc and position angle of
19 +/- 1 degrees. The ratio of non-axisymmetric to axisymmetric components
gives similar estimate for the bar size 3.3 +/- 0.1 kpc and position angle 24
+/- 2 degrees. We estimate a scale length 4.00 +/- 0.55 kpc for the IRAS
variable population, suggesting that these stars represent the old disk
population. We use this density reconstruction to estimate the optical depth to
microlensing for the large-scale bar in the Galactic disk. We find an
enhancement over an equivalent axisymmetric disk by 30% but still too small to
account for the MACHO result. In addition, we predict a significant asymmetry
at positive and negative longitudes along lines of sight through the end of the
bar with optical depths comparable to that in Baade's window. An infrared
microlensing survey may be a sensitive tool for detecting or constraining
structural asymmetries. More generally, this is a pilot study for Bayesian star
count analyses. Bayesian approach allows the assessment of prior probabilities
to the unknown parameters of the model; the resulting likelihood function is
straightforwardly modified to incorporate all available data.
 (http://xxx.lanl.gov/abs/astro-ph/9701060 ,  126kb)
\\


Paper: astro-ph/9608006
From: richard mcmahon rgm@ast.cam.ac.uk
Date: Thu, 1 Aug 1996 17:43:41 +0100 (BST)

Title: MOLECULAR GAS AND DUST AROUND A RADIO-QUIET QUASAR AT REDSHIFT 4.7
Authors: Alain Omont, Patrick Petitjean, Stephane Guilloteau, Richard G.
  McMahon, P. M. Solomon, Emmanuel Pecontal
Comments: 14 pages, 1 table, 2 figures, LaTex (aas2pp4.sty, psfig.sty), also
  available at 

http://www.ast.cam.ac.uk/~rgm
Journal-ref: Nature, 382, 428-431, 1 August 1996
\\
  We report the detection of emission from dust and carbon monoxide in the
radio-quiet quasar BR1202--0725 at redshift z=4.7. Maps of these emissions
reveal two objects separated by a few arc seconds, which could indicate either
the presence of a companion to the quasar or gravitational lensing of the
quasar itself. Regardless of the precise interpretation of the maps, the
detection of carbon monoxide confirms the presence of a large mass of molecular
gas in one of the most distant galaxies known, and shows that conditions
conducive to huge bursts of star formation existed in the early Universe.
 (http://xxx.lanl.gov/abs/astro-ph/9608006 ,  163kb)
\\


Paper: astro-ph/9604011
From: Bohdan Paczynski bp@astro.Princeton.EDU
Date: Tue, 2 Apr 1996 10:57:45 -0500 (EST)

Title: GRAVITATIONAL MICROLENSING IN THE LOCAL GROUP
Authors: Bohdan Paczynski (Princeton University Observatory)
Comments: 41 pages, latex, 13 figures, postscript version with figures
  available at http://www.astro.princeton.edu/~library/prep.html
Report-no: POPe-661
\\
  The status of searches for gravitational microlensing events of the stars in
our galaxy and in other galaxies of the Local Group, the interpretation of the
results, some theory, and prospects for the future are reviewed. The searches
have already unveiled about 100 events, at least two of them caused by
binaries, and have already proven to be useful for studies of the Galactic
structure. The events detected so far are probably attributable to the effects
of ordinary stars, and possibly to sub-stellar brown dwarfs; however a firm
conclusion cannot be reached yet because the analysis published to date is
based on a total of only 16 events. The current searches, soon to be upgraded,
will probably allow determination of the mass function of stars and brown
dwarfs in the next few years; these efforts will also provide good statistical
information about binary systems, in particular their mass ratios. They may
also reveal the nature of dark matter and allow us to detect planets and
planetary mass objects.
(http://xxx.lanl.gov/abs/astro-ph/9604011 ,  276kb)
\\


Paper: astro-ph/9606060
From: bp@astro.Princeton.EDU
Date: Mon, 10 Jun 1996 11:55:18 -0400 (EDT)

Title: THE MASSES OF NEARBY DWARFS AND BROWN DWARFS WITH THE HST
Authors: Bohdan Paczynski (Princeton University Observatory)
Comments: submitted to Acta Astronomica, 7 pages, 2 figures uuencoded, gzipped,
  tarred Latex and postscript files
\\
  The known nearby stars, moving in front of the background of distant stars
and galaxies, create 'weak gravitational lensing' variations in their
positions. These variations may be measurable with the HST, and they may allow
a direct mass determination for the nearby stars. The cross section for the HST
measurable astrometric effect is much larger than the cross section for the
photometric effect which is measurable from the ground. The mass determination
will be easier for the fainter nearby lenses which will be discovered in future
searches of faint high proper motion stars.
(http://xxx.lanl.gov/abs/astro-ph/9606060 ,  38kb)
\\


Paper: astro-ph/9609204
From: mgp@astro.Princeton.EDU
Date: Mon, 30 Sep 1996 18:04:12 -0400 (EDT)

Title: Gravitational Lensing Statistics in a Flat Universe
Authors: Myeong-Gu Park (Kyungpook National University, KOREA)
Comments: 14 pages, 3 Postscript figures, uses REVTEX. To appear in the Journal
  of Korean Physical Society
\\
  The probability distribution of lens image separations is calculated for the
``standard'' gravitational lensing statistics model in an arbitrary, flat
Robertson-Walker universe, where lensing galaxies are singular isothermal
spheres that follow the Schechter luminosity function. In a flat universe, the
probability distribution is independent of the source distribution in space and
in brightness. The distribution is compared with observed multiple-image lens
cases through Monte-Carlo simulations and the Kolmogorov-Smirnov test. The
predicted distribution depends on the shape of the angular selection bias used,
which varies for different observations. The test result also depends on which
lens systems are included in the samples. We mainly include the lens systems
where a single galaxy is responsible for lensing. We find that the ``standard''
model predicts a distribution which is different from the observed one.
However, the statistical significance of the discrepancy is not large enough to
invalidate the ``standard'' model with high confidence. Only the radio data
reject the model at the 95% confidence level, which is based on four/three lens
cases. Therefore, we cannot say that the observational data reject the
``standard'' model with enough statistical confidence. However, if we take the
velocity dispersion of dark matter without the conversion factor$ (3/2)^(1/2)$
from that of luminous matter, the discrepancy is quite severe, and even the
ground-based optical survey data reject the ``standard'' model with > ~90%
confidence.
 (http://xxx.lanl.gov/abs/astro-ph/9609204 ,  29kb)
\\


Paper: astro-ph/9702173
From: Myeong-Gu Park mgp@kyungpook.ac.kr
Date: Thu, 20 Feb 1997 05:07:35 MST   (37kb)

Title: Curvature of the Universe and Observed Gravitational Lens Image
  Separations Versus Redshift
Authors: Myeong-Gu Park, J. Richard Gott III
Comments: 21 pages, 4 figures, AASTeX4
Report-no: KNU-DAAS-97-02
\\
  In a flat, k=0 cosmology with galaxies that approximate singular isothermal
spheres, gravitational lens image separations should be uncorrelated with
source redshift. But in an open k=-1 cosmology such gravitational lens image
separations become smaller with increasing source redshift. The observed
separations do become smaller with increasing source redshift but the effect is
even stronger than that expected in an Omega=0 cosmology. The observations are
thus not compatible with the "standard" gravitational lensing statistics model
in a flat universe. We try various open and flat cosmologies, galaxy mass
profiles, galaxy merging and evolution models, and lensing aided by clusters to
explain the correlation. We find the data is not compatible with any of these
possibilities within the 95% confidence limit, leaving us with a puzzle. If we
regard the observed result as a statistical fluke, it is worth noting that we
are about twice as likely to observe it in an open universe (with 0<Omega<0.4)
as we are to observe it in a flat one. Finally, the existence of an observed
multiple image lens system with a source at z=4.5 places a lower limit on the
deceleration parameter: $q_0 > -2.0$.
 ( http://xxx.lanl.gov/abs/astro-ph/9702173 ,  37kb)
\\


Paper: astro-ph/9612062
From: Stanton Peale peale@io.ucsb.edu
Date: Thu, 5 Dec 96 21:47:35 PST

Title: Expectations from a Microlensing Search for Planets
Author: S. J. Peale (University of California at Santa Barbara)
Comments: 26 pages, LaTeX, uses aas2pp4.sty, 11 postscript figures, Submitted
  to Icarus
\\
  The statistical distribution of the masses of planets about stars between the
Sun and the center of the galaxy is constrained to within a factor of three by
an intensive search for planets during microlensing events. Projected
separations in terms of the lens Einstein ring radius yield a rough estimate of
the distribution of planetary semimajor axes with planetary mass. The search
consists of following ongoing stellar microlensing events involving sources in
the center of the galaxy lensed by intervening stars with high time resolution,
1% photometry in two colors in an attempt to catch any short time scale
planetary perturbations of the otherwise smooth light curve. It is assumed that
3000 events are followed over an 8 year period, but with half of the lenses,
those that are members of binary systems, devoid of planets. The remaining 1500
lenses have solar-system-like distributions of 4 or 5 planets. The expectations
from the microlensing search are extremely assumption dependent with 56, 138,
and 81 planets being detected for three sets of assumptions involving how the
planetary masses and separations vary with lens mass. The events can be covered
from 54% to 62% of the time on average by high time resolution photometry
from a system of three or four dedicated two meter telescopes distributed in
longitude, so 38% to 46% of the detectable small mass planets (very short
perturbations of the light curve) will be missed. But perturbations comparable
to a day in length means all of the detectable Jupiters and Saturns will in
fact be detected as well as a large fraction of the Uranuses. Although
meaningful statistics on planetary masses and separations can be inferred from
such an intensive search, they, like the inferred data set, will be dependent
on the assumed nature of the systems.
 (http://xxx.lanl.gov/abs/astro-ph/9612062 ,  175kb)
\\


Paper: astro-ph/9603146
From: roser@srvdec.obs-mip.fr (roser pello)
Date: Wed, 27 Mar 1996 19:19:46 +0200

Title: IDENTIFICATION OF A HIGH REDSHIFT CLUSTER IN THE FIELD OF Q2345+007
THROUGH DEEP BRIJK' PHOTOMETRY
Authors: R. Pello (1), J. M. Miralles (1), J.-F. Le Borgne (1), J.-P. Picat
  (2), G. Soucail (1), G. Bruzual (3) ((1) Observatoire Midi-Pyrenees LAT URA
  285, (2) Observatoire Midi-Pyrenees URA 1281, (3) Centro de Investigaciones
  de Astronomia)
Comments: 16 pages, A and A macros (l-aa.sty), 11 postcript fig. included with
  psfig, to appear in Astronomy and Astrophysics Main Journal
Report-no: MS 4721
\\
  This paper describes new results on the identification of the complex
gravita- tional lens responsible for the double quasar Q2345+007. A
gravitational shear field was detected recently about 45'' away from the QSO,
centered on an excess of faint blue galaxies. We present deep photometric data
in the near-IR (J and K'), which are used together with optical BRI photometry to
build spectral ener- gy distributions for all the objects, and to derive a
photometric redshift esti- mate by comparison with synthetic spectrophotometric
data. We propose a statis- tical method to analyse the distribution in z. An
excess of galaxies at z about 0.75 is detected in this field, with a 2D
distribution showing a maximum located at the center of the weak-shear field.
The z inferred for this overdensity (a distant cluster of galaxies) corresponds
to an absorption system in the spectrum of the quasar B. Most cluster-member
candidates at z=0.75 are undergoing a star- formation process or are burst
systems 1 to 3 Gyr old. We also discuss the exis- tence of other possible
excesses of galaxies at different z planes.
(http://xxx.lanl.gov/abs/astro-ph/9603146 ,  295kb)
\\


Paper: astro-ph/9701226
From: Avi Loeb loeb@cfata1.harvard.edu
Date: Wed, 29 Jan 1997 14:06:19 -0500   (183kb)

Title: Microlensing of Quasars By Stars In Their Damped Lyman-alpha Absorbers
Authors: Rosalba Perna and Abraham Loeb (Harvard University)
Comments: 25 pages, latex, 8 figures, submitted to ApJ
\\
  The Damped Lyman-Alpha absorbers (DLAs) in quasar spectra are believed to be
the progenitors of present-day disk galaxies. We examine the probability for
microlensing of background quasars by stars in their DLAs. Microlensing should
magnify the continuum but not the broad emission lines of the quasars. We model
a representative spiral galaxy as a closed system composed of a bulge, a disk,
and a halo, and evolve the mass fraction of stars in the disk based on the
observed metallicity of DLAs at high redshifts. The microlensing signatures are
strongly enhanced if the halo of the galaxy is made of Massive Compact Halo
Objects (MACHOs). In this case, the distortion imprinted by microlensing on the
equivalent width distribution of quasar emission lines can be detected with
high significance in a sample of <10 DLAs with HI column densities$ N>10^{21}
cm^{-2}$ and absorption redshifts z<1. About a tenth of all quasars with DLAs
$(N>10^{20} cm^{-2})$ might show excess variability on timescales shorter than
five years. A search for these signals would complement microlensing searches
in local galaxies and calibrate the MACHO mass fraction in galactic halos at
high redshifts.
 ( http://xxx.lanl.gov/abs/astro-ph/9701226 ,  183kb)
\\


Paper: astro-ph/9607082
From: Frank P. Pijpers fpp@obs.aau.dk
Date: Wed, 17 Jul 1996 07:10:34 MDT

Title: THE DETERMINATION OF TIME LAGS USING SOLA
Authors: Frank P. Pijpers (TAC, Aarhus, Denmark)
Comments: 13 pages, including figures, uses epsf.tex and mn.tex submitted to
  MNRAS
Report-no: TAC 1996-015
\\
  A common problem in astronomy is the determination of the time shift between
two otherwise identical time series of measured flux from a variable source, in
short the determination of a time lag. Two examples of where this problem
occurs are in the determination of the Hubble constant from multiple images of
gravitationally lensed variable quasars and also in the determination of
distances to OH/IR stars. It is shown here that this problem can be seen as a
restricted inversion problem. It therefore can be solved using the subtractive
optimally localized averages (SOLA) method for inversion which has been
described elsewhere (Pijpers and Thompson 1992, 1994 ; Pijpers and Wanders 1994).
 (http://xxx.lanl.gov/abs/astro-ph/9607082 ,  144kb)
\\


Paper: astro-ph/9606134
From: Mark Pratt 

mrp@darkstar.astro.washington.edu
Date: Thu, 20 Jun 1996 18:43:00 -0700

Title: THE MACHO PROJECT 2nd YEAR LMC MICROLENSING RESULTS AND DARK MATTER
IMPLICATIONS
Authors: M.R. Pratt, C. Alcock, R.A. Allsman, D. Alves, T.S. Axelrod, A.C.
  Becker, D.P. Bennett, K.H. Cook, K.C. Freeman, K. Griest, J. Guern, M.J.
  Lehner, S.L. Marshall, B.A. Peterson, P.J. Quinn, A.W. Rodgers, C.W. Stubbs,
  W. Sutherland and D.L. Welch
Comments: 10 pages, 6 epsf figures and style file included, 451k, also at

  http://wwwmacho.mcmaster.ca/Pubs/Pubs.html; To appear in the Proceedings of
  "Sources and Detection of Dark Matter in the Universe", Santa Monica, CA,
  Feb., 1996
\\
  The MACHO Project is searching for galactic dark matter in the form of
massive compact halo objects (Machos). Millions of stars in the Large
Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic bulge are
photometrically monitored in an attempt to detect rare gravitational
microlensing events caused by otherwise invisible Machos. Analysis of two years
of photometry on 8.5 million stars in the LMC reveals 8 candidate microlensing
events, far more than the $\sim1$ event expected from lensing by low-mass stars
in known galactic populations. From these eight events we estimate the optical
depth towards the LMC from events with $2 < Ts < 200$ days to be
$\tau_2^{200} \simeq 2.9 ^{+1.4}_{-0.9} 10**{-7}$. This exceeds the optical
depth of $0.5 10**{-7}$ expected from known stars and is to be compared with an
optical depth of $4.7 10**{-7}$ predicted for a ``standard'' halo composed
entirely of Machos. The total mass in this lensing population is $\approx
2^{+1.2}_{-0.7} 10**{11} M_{odot}$ (within 50 kpc from the Galactic center). Event
timescales yield a most probable Macho mass of $0.5^{+0.3}_{-0.2}M_{odot}$,
although this value is quite model dependent.
 (http://xxx.lanl.gov/abs/astro-ph/9606134 ,  233kb)
\\


Paper: astro-ph/9503020
From: joel@lick.UCSC.EDU
Date: Sat, 4 Mar 1995 11:20:52 -0800 (PST)
Date (revised): Sat, 4 Mar 1995 11:41:54 -0800 (PST)

Title: STATUS OF COSMOLOGICAL PARAMETERS: CAN $\Omega=1$?
Author: Joel R. Primack
Comments: 14 pages, uuencoded compressed .ps file
Report-no: SCIPP 95/10 (February 1995), Plenary talk at Snowmass 1994
\\
I discuss the Hubble parameter $H_0$, the age of the universe $t_0$, the
density $\Omega_0$, and the cosmological constant $\Lambda$. To focus the
discussion, I will concentrate on the issue of the value of the density
$\Omega_0$ in currently popular cosmological models in which most of the dark
matter is cold, especially Cold + Hot Dark Matter (CHDM) and flat low- $\Omega$
CDM with a Cosmological Constant ($\Lambda$CDM). The evidence would favor a
small $\Omega_0 \simeq 0.3$ if (1) the Hubble parameter actually has the high
value $h \simeq 0.8$ favored by many observers, and the age of the universe
$t_0 \geq 13$ Gy; or (2) the baryonic/total mass ratio in clusters is actually
$\sim 20$\%, about 3-4 times larger than expected for standard Big Bang
Nucleosynthesis in an $\Omega=1$ universe, and standard BBN is actually right
in predicting that the density of ordinary matter $\Omega_b$ lies in the range
$0.009 \leq \Omega_b h^2 \leq 0.02$. The evidence would favor $\Omega=1$ if (1)
the POTENT analysis of galaxy peculiar velocity data is right, in particular
regarding outflows from voids or the inability to obtain the present-epoch
non-Gaussian density distribution from Gaussian initial fluctuations in a
low-$\Omega$ universe; or (2) the preliminary report from LSND indicating a
neutrino mass $\geq 2.4$ eV is right, since that would be too much hot dark
matter to allow significant structure formation in a low-$\Omega$ $\Lambda$CDM
model. Statistics on gravitational lensing of quasars provide a strong upper
limit on $\Lambda$. Reliable data on all of these issues is becoming available
so rapidly today that a clear decision between these alternatives may be
possible within the next few years.
\\


Paper: astro-ph/9510041
From: carroll@marie.mit.edu (Sean Carroll)
Date: Fri, 6 Oct 1995 13:14:31 -0400

Title: HIGHER-ORDER GRAVITATIONAL PERTURBATIONS OF THE COSMIC MICROWAVE BACKGROUND
Authors: Ted Pyne and Sean M. Carroll
Comments: 20 pages, one figure
Report-no: MIT-CTP-2455
\\
  We study the behavior of light rays in perturbed Robertson-Walker
cosmologies, calculating the redshift between an observer and the surface of
last scattering to second order in the metric perturbation. At first order we
recover the classic results of Sachs and Wolfe, and at second order we
delineate the various new effects which appear; there is no {\it a priori}
guarantee that these effects are significantly smaller than those at first
order, since there are large length scales in the problem which could lead to
sizable prefactors. We find that second order terms of potential observational
interest may be interpreted as transverse and longitudinal lensing by
foreground density perturbations, and a correction to the integrated
Sachs-Wolfe effect. (astro-ph/9510041 ,  46kb + 20kb)
\\


Paper: astro-ph/9611118
From: Bo Qin <qin@class2.bao.ac.cn>
Date: Fri, 15 Nov 1996 15:14:46 +0800 (CST)

Title: Self-Microlensing in Compact Binary Systems
Authors: Bo Qin, Xiang-Ping Wu and Zhenlong Zou
Comments: 5 pages Latex file, Chin. Phys. Lett., in press
\\
  The signature of the self-microlensing in compact binaries (white dwarfs,
neutron stars and black holes) is a flare with the characteristic time of
typically a few minutes. The probability of detecting these microlensing events
can be as high as $1/50$ for a flux sensitivity of $\Delta m=0.01$ in
magnitude. The discovery of the self-microlensing by binaries would furnish an
additional way to find the masses of the lens and the companion and will be
promising for the searches of black holes.
 (http://xxx.lanl.gov/abs/astro-ph/9611118 ,  5kb)
\\


Paper: astro-ph/9512039
From: Avi Loeb loeb@cfata1.harvard.edu
Date: Thu, 7 Dec 1995 11:11:05 -0500

Title: PROBING CLUSTER POTENTIALS THROUGH GRAVITATIONAL LENSING OF BACKGROUND X-RAY SOURCES
Authors: Alexandre Refregier and Abraham Loeb
Comments: to appear in Proc. of "Rontgenstrahlung from the Universe" 1995, 2
  pages, 2 figures included, uuencoded compressed Postscript
\\
  We examine the gravitational lensing effect of a foreground galaxy cluster on
the number count statistics of background X-ray sources. The lensing produces a
deficit in the number of resolved sources in a ring close to the critical
radius of the cluster. This deficit could be detected at the $\sim 3\sigma$
level with the AXAF-ACIS camera.
(astro-ph/9512039 ,  46kb)
\\


Paper: astro-ph/9612102
From: rcecile@hep.saclay.cea.fr
Date: Tue, 10 Dec 1996 18:37:28 +0100

Title: Observational Limits on Machos in the Galactic Halo
Authors: EROS collaboration: C. Renault, C. Afonso, E. Aubourg, P. Bareyre, F.
  Bauer, S. Brehin, C. Coutures, C. Gaucherel, J.F. Glicenstein, B. Goldman, M.
  Gros, D. Hardin, J. de Kat, M. Lachieze-Rey, B. Laurent, E. Lesquoy, C.
  Magneville, A. Milsztajn, L. Moscoso, N. Palanque-Delabrouille, F. Queinnec,
  J. Rich, M. Spiro, L. Vigroux, S. Zylberajch, R. Ansari, F. Cavalier, F.
  Couchot, B. Mansoux, M. Moniez, O. Perdereau, J.-Ph. Beaulieu, R. Ferlet, Ph.
  Grison, A. Vidal-Madjar, J. Guibert, O. Moreau, E. Maurice, L. Prevot, C.
  Gry, S. Char, J. Fernandez
Comments: 4 pages, 3 Postscript figures, submitted to Astronomy and Astrophysics
\\
  We present final results from the first phase of the EROS search for
gravitational microlensing of stars in the Magellanic Clouds by unseen
deflectors (machos: MAssive Compact Halo Objects). The search is sensitive to
events with time scales between 15 minutes and 200 days corresponding to
deflector masses in the range 1.e-7 to a few solar masses. Two events were
observed that are compatible with microlensing by objects of mass of about 0.1
solar mass. By comparing the results with the expected number of events for
various models of the Galaxy, we conclude that machos in the mass range [1.e-7,
0.02] M$_\odot$ make up less than 20% (95% C.L.) of the Halo dark matter.
 (http://xxx.lanl.gov/abs/astro-ph/9612102 ,  29kb)

Paper: astro-ph/9612102
replaced with revised version Mon, 10 Mar 1997 12:53:13 +0100

Title: Observational Limits on Machos in the Galactic Halo
Authors: EROS collaboration: C. Renault, C. Afonso, E. Aubourg, P. Bareyre, F.
  Bauer, S. Brehin, C. Coutures, C. Gaucherel, J.F. Glicenstein, B. Goldman, M.
  Gros, D. Hardin, J. de Kat, M. Lachieze-Rey, B. Laurent, E. Lesquoy, C.
  Magneville, A. Milsztajn, L. Moscoso, N. Palanque-Delabrouille, F. Queinnec,
  J. Rich, M. Spiro, L. Vigroux, S. Zylberajch, R. Ansari, F. Cavalier, F.
  Couchot, B. Mansoux, M. Moniez, O. Perdereau, J.-Ph. Beaulieu, R. Ferlet, Ph.
  Grison, A. Vidal-Madjar, J. Guibert, O. Moreau, E. Maurice, L. Prevot, C.
  Gry, S. Char, J. Fernandez
Comments: 4 pages, 3 Postscript figures, to be published in Astronomy \&
  Astrophysics
 ( http://xxx.lanl.gov/abs/astro-ph/9612102 ,  30kb)
\\


Paper: astro-ph/9508123
From: sunhong@igpp.llnl.gov (Sun Hong Rhie)
Date: Fri, 25 Aug 1995 18:22:55 -0700

Title: INFIMUM MICROLENSING AMPLIFICATION OF THE MAXIMUM NUMBER OF IMAGES OF
  $n$-POINT LENS SYSTEMS
Authors: Sun Hong Rhie (IGPP, LLNL)
Comments: 10 pages, 1 Figure, uuencoded tar compressed postscript
\\
  The total amplification of a source inside a caustic curve of a binary lens
is no less than 3. Here we show that the infimum amplification 3 is satisfied
by a family of binary lenses where the source position is at the mid-point
between the lens positions independently of the mass ratio which parameterizes
the family. We present a new proof of an underlying constraint that the total
amplification of the two positive images is bigger than that of the three
negative images by one inside a caustic. We show that a similar constraint
holds for an arbitrary class of $n$-point lens systems for the sources in the
`maximal domains'. We introduce the notion that a source plane consists of {\it
graded caustic domains} and the `maximal domain' is the area of the source
plane where a source star results in the maximum $n^2+1$ images. We also show
that the infimum amplification of a three point lens is 7, and it is bigger
than $n^2+1-n$ for $n\ge 4$.
\\


Paper: astro-ph/9607055
From: sunhong@igpp.llnl.gov (Sun Hong Rhie)
Date: Thu, 11 Jul 1996 17:07:44 -0700 (PDT)

Title: SEARCH FOR EARTH-MASS PLANETS AND DARK MATTER, TOO
Authors: S.H.Rhie, D.P.Bennett
Comments: 5 pages, submitted to the Proceedings of the Second International
  Symposium on Sources and Detection of Dark Matter in the Universe
\\
  Gravitational microlensing is known for baryoninc dark matter searches. Here
we show that microlensing also provides a unique tool for the detection of low
mass planets (such as earths and neptunes) from the ground. A planetary system
forms a binary lens (or, a multi-point lens), and we can determine the mass
ratio of the planet with respect to the star and relative distance ($=$
separation/Einstein ring radius) between the star and planet. Such a
microlenisng planet search project requires a $\simeq 2$ m survey telescope,
and a network of $1.5-2$ m follow-up telescopes capable of monitoring stars in
the Bulge on a 24-hour basis. During the off-season of the Galactic bulge, this
network can be used for dark matter search by monitoring the stars in the LMC
and SMC.
 (http://xxx.lanl.gov/abs/astro-ph/9607055 ,  81kb)
\\


Paper: astro-ph/9603119
From: Esteban Roulet roulet@susy.he.sissa.it
Date: Thu, 21 Mar 96 16:12:43 MET

Title: MICROLENSING
Authors: E. Roulet and S. Mollerach (SISSA)
Comments: postscript file, 59 p. + 13 figures included, review to appear in
  Physics Reports
Report-no: SISSA-171/95/EP
\\
  Microlensing observations have now become a useful tool in searching for
non--luminous astrophysical compact objects (brown dwarfs, faint stars, neutron
stars, black holes and even planets). Originally conceived for establishing
whether the halo of the Galaxy is composed of this type of objects, the ongoing
searches are actually also sensitive to the dark constituents of other Galactic
components (thin and thick disks, outer spheroid, bulge). We discuss here the
present searches for microlensing of stars in the Magellanic Clouds and in the
Galactic bulge (EROS, MACHO, OGLE and DUO collaborations). We analyse the
information which can be obtained regarding the spatial distribution and motion
of the lensing objects as well as about their mass function and their overall
contribution to the mass of the Galaxy. We also discuss the additional signals,
such as the parallax due to the motion of the Earth, the effects due to the
finite source size and the lensing events involving binary objects, which can
further constrain the lens properties.
 We describe the future prospects for these searches and the further proposed
observations which could help to elucidate these issues, such as microlensing
of stars in the Andromeda galaxy, satellite parallax measurements and infrared
observations.
(http://xxx.lanl.gov/abs/astro-ph/9603119 ,  328kb)
\\


Paper: astro-ph/9702180
From: sasselov@cfassp36.harvard.edu (Dimitar Sasselov)
Date: Thu, 20 Feb 1997 18:46:13 -0500   (20kb)

Title: The Chromaticity of Microlensing (Surface Imaging of Stars)
Author: Dimitar D. Sasselov (Harvard-Smithsonian Center for Astrophysics)
Comments: 5 pages, 2 figures, LaTex, invited talk 12th IAP Colloquium on "The
  Astrophysical Returns of Microlensing Surveys", eds. R.Ferlet and
  J.P.Maillard
\\
  Gravitational microlensing is not achromatic when the star being microlensed
is resolved by the lens. We show how narrow-band photometry and moderate- to
high-resolution spectroscopy can be used to reconstruct the stellar surface
intensity distribution of a microlensed star. Such microlens imaging can
provide a unique opportunity to study the surfaces of normal red giants where
Doppler imaging is not applicable due to slow rotation.
 ( http://xxx.lanl.gov/abs/astro-ph/9702180 ,  20kb)
\\


Paper: astro-ph/9611213
From: mike@mrao.cam.ac.uk
Date: Tue, 26 Nov 96 15:50 GMT

Title: Sunyaev-Zel'dovich observations with the Ryle Telescope
Authors: Richard Saunders (MRAO, Cambridge, UK)
Comments: 5 pages, LaTex, uses 'cmb.sty' (included), 1 PostScript figure. To
  appear in proceedings of the XXXIst Rencontre de Moriond, `Microwave
  Background Anisotropies'
\\
  The Ryle Telescope has been used to provide images at 15 GHz of the
Sunyaev-Zel'dovich decrements towards a dozen clusters in an X-ray
luminosity-limited sample. So far, X-ray data have allowed $H_0$ estimates
towards two of these, both giving ``low'' values that are self-consistent,
though it is essential to obtain many more estimates to reduce the effects of
cluster projection. We have also discovered a decrement towards the z=3.8
quasar pair PC1643+4631A and B (198'' separation); substantial X-ray, optical and
infrared follow-up show that the cluster responsible is either at z>1 or very
underluminous and that very significant gravitational lensing must be occuring.
 (http://xxx.lanl.gov/abs/astro-ph/9611213 ,  14kb)
\\


Paper: astro-ph/9611219
From: mike@mrao.cam.ac.uk
Date: Tue, 26 Nov 96 18:55 GMT

Title: Optical and infrared investigation towards the z=3.8 quasar pair
  PC1643+4631A and B
Authors: Richard Saunders (1), Joanne C. Baker (1), Malcolm N. Bremer (2),
  Andrew J. Bunker (3), Garret Cotter (1), Steve Eales (4), Keith Grainge (1),
  Toby Haynes (1), Michael E. Jones (1), Mark Lacy (3), Guy Pooley (1), Steve
  Rawlings (3) ((1) MRAO Cambridge UK, (2) Leiden Observatory, (3) Oxford, (4)
  Cardiff)
Comments: 9 pages, LaTeX, 2 PostScript figures. To appear in Astrophysical
  Journal Letters
\\
  In a companion paper (Paper I: Jones et al. 1996) we report the discovery of
a cosmic microwave background decrement, indicative of a distant cluster with
mass $~10^{15}$ solar masses, towards the quasar pair PC1643+4631A and B
(z=3.79,3.83, separation 198''). To search for the cluster responsible, we have
obtained R-, J- and K-band images of the field and have also carried out
optical spectroscopy of selected objects in it. No such cluster is evident in
these images. Assuming the cluster causing the decrement is similar to massive
clusters already known, our magnitude limits imply that it must lie about or
beyond z=1. This provides independent support for the X-ray-based distance
argument of Paper I. The cluster must gravitationally lens objects behind it;
for a cluster z around 1-2, the Einstein-ring radius for sources at z ~= 3.8 is
~ 100''. Simple modelling, producing simultaneously the S-Z effect and the
lensing, shows that the source positions of quasars A and B lie within ~10'' of
each other and may indeed be coincident. The two quasar spectra are found to be
remarkably similar apart from their one-percent redshift difference. Assuming A
and B are images of a single quasar, we present a possible explanation of this
difference.
 (http://xxx.lanl.gov/abs/astro-ph/9611219 ,  130kb)
\\


Paper: astro-ph/9606101
From: saust@astro.Princeton.EDU
Date: Mon, 17 Jun 1996 13:29:25 -0400 (EDT)

Title: A STATISTICAL INVESTIGATION OF THE CONTAMINATION OF BINARY GRAVITATIONAL LENS CANDIDATES BY CATACLYSMIC VARIABLE
Author: Ann B. Saust (Princeton University Observatory)
Comments: 11 pages, LaTex, 10 PostScript files, uses aaspp.sty and psfig.
  Submitted to Astropysical Journal
\\
  A common remark at conferences and meetings has been: "One can fit any light
curve with binary lens models because of the large number of parameters!" It is
especially tempting to claim that some of the possible binary events in the
Galactic microlensing searches could be caused by cataclysmic variables since
both phenomena exhibits asymmetric light curves. This paper presents a
statistical analysis comparing the light curves of cataclysmic variable stars
to the light curves generated from binary lens models. It is shown that the
light curves of high amplitude cataclysmic variables are one example of light
curves that can not be explained with binary lens models. It is, therefore, not
only unlikely, but also impossible that cataclysmic variables can contaminate
the binary microlens candidates.
(http://xxx.lanl.gov/abs/astro-ph/9606101 ,  55kb)
\\


Paper: astro-ph/9607064
From: Sabine Schindler 

sas@MPA-Garching.MPG.DE
Date: Fri, 12 Jul 1996 13:40:28 +0200 (MDT)

Title: ROSAT/HRI STUDY OF THE OPTICALLY RICH, LENSING CLUSTER CL0500-24
Authors: Sabine Schindler, Joachim Wambsganss
Comments: 7 pages, including 5 figures, submitted to A and A
Report-no: MPE Preprint 370
\\
  An analysis of a ROSAT/HRI observation of the optically rich, gravitationally
lensing galaxy cluster CL0500-24 (or Abell S0506) is presented. We show that
the X-ray luminosity of this supposedly rich cluster is relatively low at
$1.1^{+0.2}_{-0.1}\times10^{44}$ erg/s in the ROSAT band, the bolometric X-ray
luminosity is $2.0^{+1.5}_{-0.7}\times 10^{44}$ erg/s. The X-ray emission is
strongly correlated with the northern subconcentration of the cluster galaxies
at redshift $z = 0.327$. The derived total mass of the (sub-)cluster within 1
Mpc is $(1.5\pm 0.8) \times 10^{14}$M$_\odot$, with an upper limit to the gas
mass of about $0.5\times 10^{14}$M$_\odot$, corresponding to a gas mass
fraction of $\le 30^{+30}_{-10}$\%. The X-ray luminosity and the morphology of
the extended X-ray emission supports the view that CL0500-24 consists of two
clusters at a velocity difference of $\Delta v \simeq 3200$ km/s that happen
to lie along the line of sight.
 (http://xxx.lanl.gov/abs/astro-ph/9607064 ,  217kb)
\\


Paper: astro-ph/9512047
P. Schneider peter@MPA-Garching.MPG.DE
Date: Fri, 8 Dec 1995 13:16:00 +0100 (MET)

Title: COSMOLOGICAL APPLICATIONS OF GRAVITATIONAL LENSING
Author: Peter Schneider, Max-Planck-Institut f\"ur Astrophysik, Garching,
  Germany
Comments: 26 pages, including 2 figures (a third figure can be obtained from
  the author by request) gziped and uuencoded postscript file; to be published
  in Proceedings of the Laredo Advanced Summer School, Sept. 95
Report-no: MPA 901
\\
  The last decade has seen an enormous increase of activity in the field of
gravitational lensing, mainly driven by improvements of observational
capabilities. I will review the basics of gravitational lens theory, just
enough to understand the rest of this contribution, and will then concentrate
on several of the main applications in cosmology. Cluster lensing, and weak
lensing, will constitute the main part of this review.
(astro-ph/9512047 ,  198kb)
\\


Paper: astro-ph/9601039
Peter Schneider peter@MPA-Garching.MPG.DE
Date: Wed, 10 Jan 1996 10:03:20 +0100 (MET)

Title: DETECTION OF (DARK) MATTER CONCENTRATIONS VIA WEAK GRAVITATIONAL LENSING
Author: Peter Schneider (Max-Planck-Institut f. Astrophysik, Garching, Germany)
Comments: 24 pages, Plain-Tex, no macros needed, including 10 figures,
  submitted to Monthly Notices of the Royal Astronomical Society
Report-no: MPA 917
\\
  The distortion of images of faint background galaxies by (weak) gravitational
lensing can be used to measure the mass distribution of the deflector. The
image distortions can be used to define a weighted mean of the mass inside a
circular aperture, as was first suggested by Kaiser. The aperture mass can be
used to {\it detect} dark matter concentrations. Keeping in mind that
wide-field cameras will become increasingly available, this method can be used
to search for mass concentrations on wide-field images. To do this, the
aperture mass measure is generalized to account for different weighting
functions. For each such weighting function, a signal-to-noise ratio can be
calculated. For an assumed mass profile of the density concentrations, the
weighting function can be chosen such as to maximize the resulting
signal-to-noise ratio. Numerical simulations which adopt parameters
characteristic of 4-m class telescopes are then used to show that dark halos
with a velocity dispersion in excess of $\sim 600$ km/s can be reliably
detected as significant peaks in the signal-to-noise map. The effects of seeing
and an anisotropic PSF are then investigated and shown to be less important
than might be feared. It is thus suggested that the method of aperture mass
measures developed here can be used to obtain a mass-selected sample of dark
halos, in contrast to flux-selected samples. Shear fields around high-redshift
bright QSOs as detected by Fort et al. provide a first successful application
of this strategy. The simplicity of the method allows its routine application
to wide-field images of sufficient depth and image quality.
(astro-ph/9601039 ,  157kb)
\\


Paper: astro-ph/9607095
From: Matthias Bartelmann 

msb@MPA-Garching.MPG.DE
Date: Thu, 18 Jul 1996 17:13:22 +0200 (MDT)

Title: APERTURE MULTIPOLE MOMENTS FROM WEAK GRAVITATIONAL LENSING
Authors: Peter Schneider and Matthias Bartelmann (Max-Planck-Institut fuer
  Astrophysik, Garching, Germany)
Comments: 14 pages including 3 figures, submitted to MNRAS
\\
  The projected mass of a gravitational lens inside (circular) apertures can be
derived from the measured shear inside an annulus which is caused by the tidal
field of the deflecting mass distribution. Here we show that also the
multipoles of the two-dimensional mass distribution can be derived from the
shear in annuli. We derive several expressions for these mass multipole moments
in terms of the shear, which allow large flexibility in the choice of a radial
weight function. In contrast to determining multipole moments from weak-lensing
mass reconstructions, this approach allows to quantify the signal-to-noise
ratio of the multipole moments directly from the observed galaxy ellipticities,
and thus to estimate the significance of the multipole detection. Radial weight
functions can therefore be chosen such as to optimize the significance of the
detection given an assumed radial mass profile. Application of our formulae to
numerically simulated clusters demonstrates that the quadrupole moment of
realistic cluster models can be detected with high signal-to-noise ratio S/N;
in ~ 85 per cent of the simulated cluster fields S/N >~ 3. We also show that
the shear inside a circular annulus determines multipole moments inside and
outside the annulus. This is relevant for clusters whose central region is too
bright to allow the observation of the shear of background galaxies, or which
extend beyond the CCD. We also generalize the aperture mass equation to the
case of `radial' weight functions which are constant on arbitrarily-shaped
curves which are not necessarily self-similar.
 (http://xxx.lanl.gov/abs/astro-ph/9607095 ,  64kb)
\\


Paper:astro-ph/9507093
From:T. Schramm Schramm@tu-harburg.d400.de
Date: Mon, 24 Jul 1995 12:59:14 MESZ

Title: BELTRAMI EQUATION AND CLUSTER LENSING: CHARACTERISTIC EQUATIONS AND APPLICATIONS
Author: Schramm, T
Comments: 4 pages latex, 2 figures, uuencoded, compressed tar-file
Report-no: RZ-TUHH-240795
\\
  Arclets in clusters of galaxies can be used to determine the lens mapping and
not only to constrain the mass density of the cluster. Multiply imaged arclets
are therefore easily identified without further modelling.
\\


Paper:astro-ph/9601079
From:Carolin Seitz caro@MPA-Garching.MPG.DE
Date: Mon, 15 Jan 1996 08:58:58 +0100 (MET)

STEPS TOWARDS NONLINEAR CLUSTER INVERSION THROUGH GRAVITATIONAL DISTORTIONS: III. INCLUDING A REDSHIFT DISTRIBUTION OF THE SOURCES
Authors: Carolin Seitz and Peter Schneider (Max-Planck-Institut f. Astrophysik
  Garching)
Comments: 25 pages, Plain-Tex, no macros needed, including 9 figures, submitted
  to Astronomy and Astrophysics
Report-no: MPA 920
\\
  In a series of previous papers we have considered the reconstruction of the
surface mass density of a cluster of galaxies from images of lensed faint
background galaxies. We showed that the reconstructed surface mass density is
not uniquely determined, but that there exists a global invariance
transformation that leaves the shape of the images of the lensed galaxies
unchanged. Because of this, only lower limits on the total mass of a cluster
can be derived if no further informations besides image ellipticities are used.
Throughout these papers we used the simplifying assumption that all sources are
at the same redshift. In this paper we account for a redshift distribution of
the faint galaxies, and in particular, some of these galaxies can lie in front
of the cluster or can be cluster members. We show how the mass distribution of
a cluster of galaxies can be obtained from images of these faint galaxies, if
the redshift distribution of these galaxies is known. We demonstrate that for
the reconstruction of non-critical clusters we need less information on the
redshift distribution of the galaxies, i.e., we only need to know two or three
moments of the distribution. We show that the mean mass density across the data
field is still a free variable, i.e., there remains a global invariance
transformation of the resulting mass density field. For non-critical clusters
we can derive the transformation explicitly and it is similar to that derived
previously for the case of a single redshift of the sources. We discuss several
theoretical ideas to break the mass degeneracy; of those considered, we find
that only the magnification effect on the number density of galaxy images can
be used successfully in practice. (astro-ph/9601079 ,  181kb)
\\


Paper: astro-ph/9602105
From: squires@magicbean.berkeley.edu (Gordon Squires)
Date: Tue, 20 Feb 1996 14:18:04 -0800

Title: A WEAK GRAVITATIONAL LENSING ANALYSIS OF ABELL 2390
Authors: G.Squires, N. Kaiser, G. Fahlman, A. Babul, D. Woods 
Comments: 14 pages, latex file. Postscript file also available at
\\
ftp://magicbean.berkeley.edu/pub/squires/a2390/massanlight.ps.gz
Report-no: CfPA 96-th-07
\\
  We report on the detection of dark matter in the cluster Abell 2390 using the
weak gravitational distortion of background galaxies. We find that the cluster
light and total mass distributions are quite similar over an angular scale of
$\simeq 7^\prime \;(1 Mpc$). The cluster galaxy and mass distributions are
centered on the cluster cD galaxy and exhibit elliptical isocontours in the
central $\simeq 2^\prime \; (280 kpc)$. The major axis of the ellipticity is
aligned with the direction defined by the cluster cD and a ``straight arc''
located $\simeq 38^{\prime\prime}$ to the northwest. We determined the radial
mass-to-light profile for this cluster and found a constant value of $(320 \pm
90) h\; M_\odot/L_{\odot V}$, which is consistent with other published
determinations. We also compared our weak lensing azimuthally averaged radial
mass profile with a spherical mass model proposed by the CNOC group on the
basis of their detailed dynamical study of the cluster. We find good agreement
between the two profiles, although there are weak indications that the CNOC
density profile may be falling more steeply for $\theta\geq 3^\prime$
$(420 kpc)$.  (http://xxx.lanl.gov/abs/astro-ph/9602105 ,  41kb)
\\


Paper: astro-ph/9603050
From: squires@magicbean.berkeley.edu (Gordon Squires)
Date: Tue, 12 Mar 1996 10:14:35 -0800

Title: A WEAK GRAVITATIONAL LENSING AND X-RAY ANALYSIS OF ABELL 2163
Authors: G. Squires, D. M. Neumann, N. Kaiser, M. Arnaud, A. Babul, H.
  B\"ohringer, G. Fahlman, and D. Woods
Comments: 30 pages, latex file. Postscript file also available at
\\
ftp://magicbean.berkeley.edu/pub/squires/a2163/a2163{\_}paper.ps.gz
Report-no: CfPA 96-th-09
\\
  We report on the detection of dark matter in the cluster of galaxies
Abell~2163 using the weak gravitational distortion of background galaxies, and
an analysis of the cluster X-ray emission. We find that while the qualitative
distributions of the cluster light and the dark matter are similar -- shallow
and extended, with significant substructure -- the X-ray morphology shows a
more regular overall appearance. We interpret the joint lensing and X-ray
observations as a signature of a merger event in the cluster. We present new
ROSAT/HRI data and reanalyze ROSAT/PSPC data, accounting for the effect of a
varying background to determine the best fit parameters in the $\beta$-model
formalism. We combine the surface brightness fits with two determinations of
the radial temperature profile to determine the total mass. Although there are
slight variations in the total mass determinations introduced by the
uncertainties in the $\beta$-fit, the main contributor to the error arises from
the uncertainties in the temperature determinations. Even though the
morphologies of the dark matter/light and X-ray gas are quite different, we
find that the total mass determined from the X-ray and weak lensing estimates
are consistent with each other within the $2\sigma$ error bars, with the X-ray
inferred mass a factor of $\simeq 2$ larger. However, as the lensing mass
estimates are differential (the surface density at any point is determined
relative to the mean in a control annulus), the shallow, extended nature of the
mass profile biases the lensing inferred mass downwards. We estimate the
correction for this effect and find very good agreement between the corrected
lensing and X-ray results. We determine the gas mass fraction and find $f_g
\simeq 0.07h^{-3/2}$ at all radii and a constant mass-to-light ratio of $M/L_V$
(http://xxx.lanl.gov/abs/astro-ph/9603050 ,  372kb)
\\


Paper: astro-ph/9609149
From: Albert Stebbins stebbins@perseus.fnal.gov
Date: Sun, 22 Sep 1996 17:14:56 -0500

Title: Weak Lensing On the Celestial Sphere
Authors: Albert Stebbins
Comments: 27 pages, plain TeX, 7 figures, submitted to The Astrophysical
  Journal, PostScript version with embedded figures available from
  http://www-astro-theory.fnal.gov/Publications/Pub-96-328-A/
Report-no: FERMILAB-Pub-96/328-A
\\
  This paper details a description of the pattern of galaxy image distortion
over the entire sky caused by the gravitational lensing which is the result of
large scale inhomogeneities in our universe. We present a tensor spherical
harmonic formalism to describe this pattern, giving many useful formulae. This
is applied to density inhomogeneities, where we compute the angular power
spectrum of the shear pattern, as well as the noise properties due to finite
galaxy sampling and cosmic variance. We show that a detectable level of shear
is present for very nearby galaxies, $z\simeq0.2$. For such a shallow sample
much of the largest signal-to-noise comes from very large angular scales,
$\theta > 10^\circ$, although it is in the form of very small shear at a
level $\simeq10^{-3}$.
 (http://xxx.lanl.gov/abs/astro-ph/9609149 ,  257kb)
\\


Paper: astro-ph/9703103
From: Marcus Straessle marcus@physik.unizh.ch
Date: Mon, 17 Mar 97 14:12:23 MET   (22kb)

Title: Complex Formulation of Lensing Theory and Applications
Author: Norbert Straumann (University of Zurich)
Comments: 12 pages, REVTeX, two postscript figures included
Report-no: ZU-TH 7/97
\\
  The elegance and usefulness of a complex formulation of the basic lensing
equations is demonstrated with a number of applications. Using standard tools
of complex function theory, we present, for instance, a new proof of the fact
that the number of images produced by a regular lens is always odd, provided
that the source is not located on a caustic. Several differential and integral
relations between the mean curvature and the (reduced) shear are also derived.
These emerge almost automatically from complex differentiations of the
differential of the lens map, together with Stokes' theorem for complex valued
1-forms.
 ( http://xxx.lanl.gov/abs/astro-ph/9703103 ,  22kb)
\\


Paper: astro-ph/9611059
From: Will Sutherland 

w.sutherland1@physics.oxford.ac.uk
Date: Thu, 7 Nov 1996 19:47:28 +0000 (GMT)

Title: Gravitational Microlensing Results from MACHO
Authors: The MACHO Collaboration: W. Sutherland, C. Alcock, R.A. Allsman, D.
  Alves, T.S. Axelrod, A.C. Becker, D.P. Bennett, K.H. Cook, K.C. Freeman, K.
  Griest, J. Guern, M.J. Lehner, S.L. Marshall, B.A. Peterson, M.R. Pratt, P.J.
  Quinn, A.W. Rodgers, C.W. Stubbs, D.L. Welch
Comments: Latex, 12 pages, uses sprocl.sty (included), with 5 Postscript
  figures. To appear in proceedings of workshop on ``Identification of Dark 
  Matter'', Sheffield, Sep. 1996
\\
  The MACHO project is searching for dark matter in the form of massive compact
halo objects (Machos), by monitoring the brightness of millions of stars in the
Magellanic Clouds to search for gravitational microlensing events. Analysis of
our first 2.3 years of data for 8.5 million stars in the LMC yields 8 candidate
microlensing events, well in excess of the $\simeq 1$ event expected from
lensing by known low-mass stars. The event timescales range from 34 to 145
days, and the estimated optical depth is $\sim 2 x 10^{-7}$, about half of that
expected from a `standard' halo. Likelihood analysis indicates the typical lens
mass is $0.5^{+0.3}_{-0.2} Msun$, suggesting they may be old white dwarfs.
 (http://xxx.lanl.gov/abs/astro-ph/9611059 ,  150kb)
\\


Paper: astro-ph/9608173
From: Max Tegmark max@mppmu.mpg.de
Date: Tue, 27 Aug 1996 12:56:37 +0200

Title: Is lensing of point sources a problem for future CMB experiments?
Authors: Max Tegmark and Jens Villumsen
Comments: 13 pages, with 3 figures included. Latest version and color figures
  at 

http://www.sns.ias.edu/~max/lensing.html (faster from the US), from
http://www.mpa-garching.mpg.de/~max/lensing.html (faster from Europe) or from
  max@ias.edu
\\
  No. Weak gravitational lensing from large-scale structure enhances and
reduces the fluxes from extragalactic point sources with an rms amplitude of
order 15%. In cosmic microwave background (CMB) experiments, all sources
exceeding some flux threshold are removed, which means that lensing will
modulate the brightness map of the remaining unresolved sources. Since this
mean brightness is of order 100 micro-Kelvin at 30 GHz for a reasonable flux
cut, one might be concerned that this modulation could cause substantial
problems for future CMB experiments. We present a detailed calculation of this
effect and, fortunately, find that its power spectrum is always smaller than
the normal point source power spectrum. Thus although this effect should be
taken into account in a detailed CMB analysis, it will not substantially reduce
the accuracy with which cosmological parameters can be measured.
 (http://xxx.lanl.gov/abs/astro-ph/9608173 ,  55kb)
\\
Paper: astro-ph/9608173
replaced with revised version Wed, 26 Mar 1997 17:41:02 +0100

Title: Is lensing of point sources a problem for future CMB experiments?
Authors: Max Tegmark, Jens Villumsen
Comments: Expanded to match published version. 14 pages, with 3 figures
  included. Color figures at http://www.sns.ias.edu/~max/lensing.html (faster
  from the US), from http://www.mpa-garching.mpg.de/~max/lensing.html (faster
  from Europe) or from max@ias.edu
 ( http://xxx.lanl.gov/abs/astro-ph/9608173 ,  58kb)
\\


Paper: astro-ph/9702084
From: Philippe Jetzer jetzer@sonne.physik.unizh.ch
Date: Mon, 10 Feb 1997 14:13:47 +0100   (7kb)

Title: Achromatic variability in the BL Lac object PKS 2155-304. A case for
  microlensing?
Authors: A. Treves, F. Rovetti, Ph. Jetzer and C.M. Urry
Comments: 11 pages, no figures, Latex
\\
  PKS 2155-304 is the only BL Lac object for which well-sampled multiwavelength
light curves resolve the intraday variability at UV and X-ray wavelengths. In
particular we focus on the multifrequency campaign of November 1991, which
showed a rather exceptional behaviour of the source exhibiting substantial
achromatic variability from optical to X-ray wavelengths. We suggest a scenario
for this unique event, where the variability is due to microlensing. The
relativistic motion of the source relative to the lens is taken into account.
The lenses are proposed to be solar-mass stars in an intervening dwarf galaxy.
The a priori probability of detecting a microlensing event, however, was only
few percent, small but not negligible.
 ( http://xxx.lanl.gov/abs/astro-ph/9702084 ,  7kb)
\\


Paper: astro-ph/9601168
From: Geza Gyuk gyuk@oddjob.uchicago.edu
Date: Mon, 29 Jan 1996 17:09:39 -0600

Title: MACHOs: THE PLOT THICKENS
Authors: Michael S. Turner, Evalyn I. Gates and Geza Gyuk
Comments: 6 pages, two figures, postscript
Report-no: FERMILAB--Pub--96/022-A
\\
  We discuss the implications of the recent upward revision of the LMC
microlensing rate by the MACHO Collaboration. We conclude: (i) A good case for
the existence of baryonic dark matter in the halo has been made; (ii) The case
for the existence of cold dark matter is unaffected and still compelling; and
(iii) The Galactic halo is still an excellent place to search for cold dark
matter particles (e.g., axions or neutralinos).
 (http://xxx.lanl.gov/abs/astro-ph/9601168 ,  31kb)
\\


Paper: astro-ph/9601113
From: E.Kampen@roe.ac.uk
Date: Mon, 22 Jan 96 15:25:22 GMT

Title: THE AMPLITUDE OF THE INITAIL DENSITY FLUCTUATION SPECTRUM FROM LRNSING STATISTICA''
Authors: Eelco van Kampen (Royal Observatory Edinburgh, U.K.)
Comments: 6 pages including 3 figures, gzip'ed and uuencoded Postscript, To
  appear in proceedings "Mapping, Measuring and Modelling the Universe",
  Valencia 1995, eds. P. Coles and V. Martinez
\\
  A complete catalogue of galaxy cluster models can be used to constrain
cosmological parameters like $\sigma_8$, the amplitude of the initial density
fluctuation spectrum. We focus here on two strong lensing statistics for
clusters of galaxies: the fraction of rich Abell clusters that are critical to
lensing, and the abundance of arcs in such clusters, especially the X-ray
luminous ones. The specific aim of this paper is to constrain $\sigma_8$ for
the standard Cold Dark Matter scenario within an Einstein-de Sitter universe.
(http://xxx.lanl.gov/abs/astro-ph/9601113 ,  109kb)
\\


Paper: astro-ph/9606100
From: waerbeke@srvdec.obs-mip.fr (p'ti lu)
Date: Mon, 17 Jun 1996 16:53:06 +0200

Title: WEAK LENSING AS A PROBE OF DARK MATTER
Authors: L. Van Waerbeke (OMP, Toulouse, France) and Y. Mellier (IAP, Paris,
  France)
Comments: 8 pages, Latex with 2 included postscript figures, 1 55kB JPEG figure
  (also available as (1.1MB) compressed ps file from anonymous ftp at
  ftp://summer.obs-mip.fr/pub/OUTGOING/ludo/simul.ps.Z), to be published in the
  proceedings of the XXXIst Rencontres de Moriond, Les Arcs, France, January
  20-27 1996
\\
  Weak gravitational lensing of distant galaxies can probe the total projected
mass distribution of foreground gravitational structures on all scales and has
been used successfully to map the projected mass distribution of rich
intermediate redshift clusters. This paper reviews the general concepts of the
lensing analysis. We focus on the relation between the observable (shapes and
fluxes) and physical (mass, redshift) quantities and discuss some observational
issues and recent developments on data analysis which appear promising for a
better measurement of the lensing signatures (distortion and magnification) at
very large scales.
(http://xxx.lanl.gov/abs/astro-ph/9606100 ,  74kb)
\\


Paper: astro-ph/9604137
From: waerbeke@srvdec.obs-mip.fr (p'ti lu)
Date: Tue, 23 Apr 1996 17:05:32 +0200 (MET DST)

Title: THE AUTO-CORRELATION FUNCTION OF THE EXTRAGALACTIC BACKGROUND LIGHT: I.
  MEASURING GRAVITATIONAL SHEAR
Authors: L. Van Waerbeke (1) Y. Mellier (1,2,3) P. Schneider (4) B. Fort (3) G.
  Mathez (1) ((1) Observatoire Midi-Pyrenees LAT URA 285, (2) Institut
  d'Astrophysique de Paris, (3) DEMIRM, Observatoire de Paris, (4)
  Max-Planck-Institut f\"ur Astrophysik.)
Comments: 14 pages, A and A macros (l-aa.sty), postscript figs available from
  anonymous ftp at ftp://summer.obs-mip.fr/pub/OUTGOING/ACFfigs, Submitted to
  Astronomy and Astrophysics Main Journal
\\
  A new method for measuring the shear induced by gravitational light
deflection is proposed. It is based on analyzing the anisotropy induced in the
auto-correlation function (ACF) of the extragalactic background light which is
produced by very faint distant galaxies. The ACF can be measured `locally', and
its anisotropy is caused by the tidal gravitational field of the deflecting
mass distribution in the foreground of these faint background galaxies. Since
the method does not require individual galaxy detection, it can be used to
measure the shear of extremely faint galaxies which are not detectable
individually, but are present in the noise. The shear estimated from the ACF of
the noise provides an independent measurement which can be compared to the
shear obtained from the distortion of individual galaxy images. Combining these
two independent estimates clearly increases the sensitivity of shear
measurements. In addition, our method may allow to determine the local
magnification caused by the deflector if the auto-correlation function is
caused by a large number density of faint galaxies; in this case, the intrinsic
ACF may provide a `standard source' with respect to which shear and
magnification can be obtained. Applications to real and synthetic data are
shown and the feasibility of our new method is demonstrated. In particular, we
present the shear maps obtained with our method for the double QSO 2345+007 and
the cluster Cl0024+16 and compare them to published shear maps.
(http://xxx.lanl.gov/abs/astro-ph/9604137 ,  36kb)
\\


Paper: astro-ph/9605113
From: jmq@gamma.uchicago.edu (Jean M. Quashnock)
Date: Fri, 17 May 96 16:59:18 CDT

Title: AN EXCESS OF CIV ABSORBERS IN LUMINOUS QSOS: EVIDENCE FOR GRAVITATIONAL LENSING?
Authors: Daniel E. Vanden Berk, Jean M. Quashnock, Donald G. York, (Dept. of
  Astronomy and Astrophysics, U. Chicago), and Brian Yanny (Fermilab)
Comments: 21 LaTeX pages with 5 encapsulated Postscript figures included, uses
  AASTeX (v. 4.0) available at ftp://ftp.aas.org/pubs/ , to appear in The
  Astrophysical Journal, Sept. 20, 1996
\\
  We have compiled a new and extensive catalog of heavy-element QSO absorption
line systems and analyzed the distribution of absorbers in bright and faint
QSOs, to search for gravitational lensing of background QSOs by the matter
associated with the absorbers. There is a highly significant excess of C {\sc
iv} absorbers in bright QSOs in the redshift range $z=1.2-3.2$, and this excess
increases strongly as a function of QSO absolute magnitude. No significant
excess is found for Mg {\sc ii} absorbers in the redshift range $z=0.30-1.55$.
We rule out several possible reasons for this effect and argue that the C {\sc
iv} excess could be due to gravitational lensing. If so, then the lensing
masses must be at $z \geq 1.5$ and within several hundred comoving Mpc of
the QSOs, where the C {\sc iv} absorbers are mainly found. The absence of an
excess in the available Mg {\sc ii} sample would then arise because the Mg {\sc
ii} data does not sample this region of space.
(http://xxx.lanl.gov/abs/astro-ph/9605113 ,  202kb)
\\


Paper: astro-ph/9606084
From: Jens Villumsen jens@MPA-Garching.MPG.DE
Date: Thu, 13 Jun 1996 18:07:41 +0200

Title: CLUSTERING OF GALAXIES IN THE HUBBLE DEEP FIELD
Authors: Jens V. Villumsen (Max-Planck-Institut f\"ur Astrophysik), Wolfram
  Freudling (Space Telescope--European Coordinating Facility and European
  Southern Observatory), Luiz N. da Costa(European Southern Observatory and
  Observatorio Nacional, Rio de Janeiro, Brazil)
Comments: 9 pages, Latex, [aas2pp4], 5 Postscript figures. Figures obtainable
  via anonymous FTP from ftp://ecf.hq.eso.org/pub/preprints/hdf Submitted to
  Astrophysical Journal. jens@mpa-garching.mpg.de
\\
  We compute the two-point angular correlation function w for a sample of
$\sim$ 1700 galaxies to a magnitude-limit equivalent of $R~\sim~29.5$ using a
catalog derived from the Hubble Deep Field images. A non zero value of w is
measured down to $R=29.0$. The amplitude of w at the bright magnitude limit,
($R~\sim~26$), is consistent with previous ground-based observations. At
fainter magnitudes the clustering amplitude continues to decrease but at a
slower rate than that predicted by the power law $w(1'')\propto 10^{-0.27R}$
observed for shallower samples. The observed w over the magnitude range $20\
<R<\ 29$ is consistent with linear evolution of the clustering of a galaxy
population which at present has a correlation length $r_0$ of about 4 h1 Mpc,
close to that of local {\it IRAS} galaxies. We also investigate the impact that
magnification bias induced by weak gravitational lensing may have on our
results. Although the observed amplitude of w can differ from the true
amplitude by up to 30\%, this effect is not large enough to affect our
conclusions. Finally, by using a color-selected sample we examine whether the
expected effects of magnification bias can be used for an independent
determination of cosmological parameters in deep images. We conclude that the
amplitude of the effect can be large and in some cases even produce an upturn
of the amplitude of the correlation with limiting magnitude. However, we
conclude that from the observed w, it is not possible to unequivocably detect
the effects of magnification bias. We suggest that with redshift information,
it is possible to measure the effects of magnification bias directly and thus
have an alternative way of constraining $\Omega_0/b$, where $\Omega_0$ is the
density parameter and $b$ is the biasing factor.
(http://xxx.lanl.gov/abs/astro-ph/9606084 ,  14kb)
\\


Paper:astro-ph/9512001
From:J. Villumsen jens@MPA-Garching.MPG.DE
Date: Fri, 1 Dec 1995 16:08:42 +0100 (MET)

Title: CLUSTERING OF FAINT GALAXIES: ?? INDUCED BY WEAK GRAVITATIONAL LENSING
Author: Jens Verner Villumsen (Max Planck Institute fur Astrophysik, Garching,
  Germany)
Comments: 11 pages, 2 figures, Submitted to: Monthly Notices of the Royal
  Astronomical Society
\\
  Weak gravitational lensing by large scale structure affects the number counts
of faint galaxies through the ``magnification bias'' and thus affects the
measurement of the angular two-point correlation function ??. At faint
magnitudes the clustering amplitude will decrease differently with limiting
magnitude than expected from Limber's equation. The amplitude will hit a
minimum and then rise with limiting magnitude. This behavior occurs because
?? due to clustering decreases with distance, while the ``magnification
bias'' due to weak lensing increases with distance. The apparent magnitude
$m_{min}$ at which the magnification bias starts to dominate the observed
clustering is model and color dependent. It is given by
$\omega(m=m_{min},\theta=5^\prime) \simeq (1\ -\ 2)\times 10^{-3}(5s-2)^2
\Omega_0^2 \sigma_8^2$, where $s$ is the logarithmic slope of the number
counts. Already published measurements of ?? at $R=25$ may be strongly
influenced by the ``magnification bias''. An experiment using the ratio of blue
and red number counts across the sky can be designed such that the effects of
the ``true'' clustering is minimized. The magnification bias is a measurement
of the clustering of the mass. This weak lensing experiment does not require
measuring shapes and position angles of galaxies. I derive a revised Limber's
Equation including the effects of magnification bias.
(astro-ph/9512001 ,  47kb + 38kb)
\\


Paper:astro-ph/9511137
From:Chris Kochanek kochanek@cfa.harvard.edu
Date: Tue, 28 Nov 1995 09:03:05 -0500

Title: LensMEM: A GRAVITATIONAL LENS INVERSION ALGORITHM USING THE MAXIMUM ENTROPY METHOD
Author: S. Wallington, C.S. Kochanek and R. Narayan (Harvard-Smithsonian Center
  For Astrophysics)
Comments: 27 pages, uuencoded, gzip compressed postscript
\\
  We present a new algorithm for inverting poorly resolved gravitational lens
systems using the maximum entropy method (MEM). We test the method with
simulations and then apply it to an 8 GHz VLA map of the radio ring lens
MG1654+134. We model the lens as a singular isothermal sphere embedded in an
external shear field and find the critical radius of the lens is
$b=0 parcs$, the dimensionless shear is $\gamma=0.0771$, and the position
angle of the shear is $\theta=100 deg$. These results are consistent with the
results obtained by Kochanek (1995) using a complementary inversion algorithm
based on Clean.
(astro-ph/9511137 ,  211kb)
\\


Paper: astro-ph/9610096
From: Joachim Wambsganss jwambsganss@aip.de
Date: Mon, 14 Oct 1996 15:39:54 +0100

Title: Testing Cosmological Models by Gravitational Lensing: I. Method and
  First Applications
Authors: Joachim Wambsganss(1,2), Renyue Cen(2) and Jeremiah P. Ostriker (2)
  (1-Astrophysikalisches Institut Potsdam, 2-Princeton University Observatory)
Comments: submitted to ApJ; 25 pages plus 11 Figures (partly in JPEG/GIF format
  due to size constraints). Postscript files of all figures can be downloaded
  at http://astro.princeton.edu/~cen/LENS\_METHOD/lens\_method.html (USA) or
  
http://www.aip.de:8080/~jkw/method\_figures.html (Germany). Hardcopies of the
  (color) figures can be obtained on request by J.W
\\
  Gravitational lensing directly measures mass density fluctuations along the
lines of sight to very distant objects. No assumptions need to be made
concerning bias, the ratio of fluctuations in galaxy density to mass density.
Hence, lensing is a very useful tool to study the universe at low to moderate
redshifts.
  We describe in detail a new method to trace light rays from redshift zero
through a three dimensional mass distribution to high redshift. As an example,
this method is applied here to a standard cold dark matter universe. We obtain
a variety of results, some of them statistical in nature, others from rather
detailed case studies of individual ``lines of sight". Among the former are the
frequency of multiply imaged quasars, the distribution of separation of the
multiple quasars, and the redshift distribution of lenses: all that as a
function of quasar redshift. We find effects from very weak lensing to highly
magnified multiple images of high redshift objects, which, for extended
background sources, (i.e. galaxies), range from slight deformations of the
shapes through tangentially aligned arclets up to giant luminous arcs.
  Different cosmological models differ, increasingly with redshift, in their
predictions for the mass (thus gravitational potential) distributions. Our
ultimate goal is to apply this method to a number of cosmogonic models and to
eliminate some models whose gravitational lensing properties are inconsistent
with those observed.
 (http://xxx.lanl.gov/abs/astro-ph/9610096 ,  459kb)
\\


Paper: astro-ph/9605140
From: Yun Wang ywang@fnas07.fnal.gov
Date: Wed, 22 May 1996 17:41:15 -0500

Title: GRAVITATIONAL LENSING OF GRAVITATIONAL WAVES FROM MERGING NEUTRON STAR BINARIES
Authors: Yun Wang, Albert Stebbins, and Edwin L. Turner
Comments: REVTeX, 13 pages including 3 figures. Submitted to Phys. Rev. Lett
Report-no: Fermilab-Pub-96/091-A
\\
  We discuss the gravitational lensing of gravitational waves from merging
neutron star binaries, in the context of advanced LIGO type gravitational wave
detectors. We consider properties of the expected observational data with cut
on the signal-to-noise ratio $\rho$, i.e., $\rho>\rho_0$. An advanced LIGO
should see unlensed inspiral events with a redshift distribution with cut-off
at a redshift $z_{\rm max} < 1$ for $h \leq 0.8$. Any inspiral events detected
at $z>z_{\rm max}$ should be lensed. We compute the expected total number of
events which are present due to gravitational lensing and their redshift
distribution for an advanced LIGO in a flat Universe. If the matter fraction in
compact lenses is close to 10\%, an advanced LIGO should see a few strongly
lensed events per year with $\rho >5$.
(http://xxx.lanl.gov/abs/astro-ph/9605140 ,  36kb)
\\


Paper: astro-ph/9607076
From: Yun Wang ywang@fnas07.fnal.gov
Date: Mon, 15 Jul 96 19:38:10 -0500

Title: STATISTICS OF EXTREME GRAVITATIONAL LENSING EVENTS. II.THE SMALL SHEAR CASE
Authors: Yun Wang (Fermilab) and Edwin L. Turner (Princeton)
Comments: 17 pages including 3 figures, using AAS LATEX macros v4.0. Submitted
  to ApJ
Report-no: FERMILAB-Pub-96/060-A
\\
  We consider an astrophysical system with a population of sources and a
population of lenses. For each pair of source and lens, there is a thin on-axis
tube-like volume behind the lens in which the radiation flux from the source is
greatly increased due to gravitational lensing. Any objects (such as dust
grains) which pass through such a thin tube will experience strong bursts of
radiation, i.e., Extreme Gravitational Lensing Events (EGLE). We study the
physics and statistics of EGLE for the case in which the shear is larger or
comparable to the finite source size. We find that the presence of shear has
only a small effect on the EGLE statistics.
 (http://xxx.lanl.gov/abs/astro-ph/9607076 ,  50kb)
\\


Paper: astro-ph/9701230
From: ywang@astro.Princeton.EDU
Date: Wed, 29 Jan 1997 19:27:26 -0500 (EST)   (7kb)

Title: Astrophysical Effects of Extreme Gravitational Lensing Events
Authors: Yun Wang and Edwin L. Turner (Princeton)
Comments: 3 pages including 1 figure, LaTeX. To appear in the Proceedings of
  the 18th Texas Symposium, World Scientific Press (editors A. Olinto, J.
  Frieman, and D. Schramm)
\\
  Every astrophysical object (dark or not) is a gravitational lens, as well as
a receiver/observer of the light from sources lensed by other objects in its
neighborhood. For a given pair of source and lens, there is a thin on-axis
tubelike volume behind the lens in which the radiation flux from the source is
greatly increased due to gravitational lensing. Any objects which pass through
such a thin tube or beam will experience strong bursts of radiation, i.e.,
Extreme Gravitational Lensing Events (EGLEs). We have studied the physics and
statistics of EGLEs. EGLEs may have interesting astrophysical effects, such as
the destruction of dust grains, ignition of masers, etc. Here we illustrate the
possible astrophysical effects of EGLEs with one specific example, the
destruction of dust grains in globular clusters.
 ( http://xxx.lanl.gov/abs/astro-ph/9701230 ,  7kb)
\\


Paper: astro-ph/9702078
From: ywang@astro.Princeton.EDU
Date: Sun, 9 Feb 1997 19:33:31 -0500 (EST)   (105kb)

Title: Caustics, Critical Curves and Cross Sections for Gravitational Lensing
  by Disk Galaxies
Authors: Yun Wang and Edwin L. Turner (Princeton)
Comments: 31 pages including 15 figure, LaTeX
\\
  We study strong gravitational lensing by spiral galaxies, modeling them as
infinitely thin uniform disks embedded in singular isothermal spheres. We
derive general properties of the critical curves and caustics analytically. The
multiple-image cross section is a sensitive function of the inclination angle
of the disk relative to the observer. We compute the inclination averaged cross
section for several sets of lensing parameters. For realistic disk mass and
size parameters, we find that the cross section for multiple imaging is
increased by only a modest factor and {\it no} dramatic increase in the optical
depth for strong lensing of QSOs would be expected. However, the cross section
for high magnifications is significantly increased due to the inclusion of a
disk, especially for nearly edge-on configurations; due to the strong
observational selection effects favoring high magnifications, there might be
significant consequences for lensing statistics.
 ( http://xxx.lanl.gov/abs/astro-ph/9702078 ,  105kb)
\\


Paper: astro-ph/9608044
From: swhite@iris-6.MPA-Garching.MPG.DE (Simon White)
Date: Fri, 9 Aug 1996 19:07:16 +0200

Title: Large-scale structure at high redshift
Author: Simon D.M. White (MPA, Garching)
Comments: 12 pages. Invited review for the ESO Workshop on "The Early Universe
  with the VLT" 1-4 April 1996. The three colour figures are available at
  high resolution from http://www.mpa-garching.mpg.de/~swhite
\\
  I discuss and illustrate the development of large-scale structure in the
Universe, emphasising in particular the physical processes and cosmological
parameters that most influence the observationally accessible aspects of
structure at large redshift. Statistical properties of this structure can be
measured from the apparent positions of faint galaxies and quasars; the
structure can be mapped in three dimensions by obtaining redshifts for large
samples of such objects; it can be studied using foreground absorption in the
spectra of quasars; finally the mass distribution can be constrained by
measuring the gravitationally induced distortion of background galaxy images.
The first and last of these techniques require deep imaging of large areas of
the sky with the best possible image quality. The second and third will require
8m-class telescopes with efficient multiobject spectrographs. For QSO
absorption line spectroscopy high spectral resolution is also important.
 (http://xxx.lanl.gov/abs/astro-ph/9608044 ,  22kb)
\\


Paper: astro-ph/9701246
From: llrw@ast.cam.ac.uk (Liliya L.R. Williams)
Date: Thu, 30 Jan 1997 21:55:09 GMT   (74kb)

Title: Distortion of gamma-ray burst light curves by gravitational microlensing
Authors: L. L. R. Williams and R. A. M. J. Wijers (Institute of Astronomy,
  Cambridge, UK)
Comments: 6 pages when LaTex'ed, with 5 figures included Accepted to MNRAS
\\
  If at cosmological distances, a small fraction of gamma-ray bursts should be
multiply imaged by intervening galaxies or clusters, resulting in the
appearance of two very similar bursts from the same location with a relative
time delay of hours to a year. We show that microlensing by individual stars in
the lensing galaxy can smear out the light curves of the multiply imaged bursts
on millisecond time scales. Therefore, in deciding whether two bursts are
similar enough to qualify as multiple images, one must look at time scales
longer than a few tens of milliseconds, since shorter time scales are possibly
rendered dissimilar by microlensing.
 ( http://xxx.lanl.gov/abs/astro-ph/9701246 ,  74kb)
Paper: astro-ph/9701246
replaced with revised version Mon, 3 Feb 1997 22:31:32 GMT

Title: Distortion of gamma-ray burst light curves by gravitational microlensing
Authors: L. L. R. Williams and R. A. M. J. Wijers (Institute of Astronomy,
  Cambridge, UK)
Comments: 6 pages when LaTex'ed, with 5 figures included Accepted to MNRAS;
  replaced version contains psfigure.tex file, since psfig.tex was causing
  problems (no changes in the text or figures of the paper)
 ( http://xxx.lanl.gov/abs/astro-ph/9701246 ,  84kb)
\\

Paper: astro-ph/9702021
From: Hans Joerg Witt hwitt@aip.de
Date: Mon, 3 Feb 97 13:45:01 +0100   (44kb)

Title: Probing the Structure of Lensing Galaxies with Quadruple Lenses: The
  Effect of the ``External'' Shear
Author: Hans J. Witt (Astrophysical Institute Potsdam) and Shude Mao (MPA,
  Garching)
Comments: 16 pages including 3 Postscript figures, uses MN-Latex, submitted to
  MNRAS
\\
  We study a general elliptical potential of the form $\psi(x^2+y^2/q^2)~
(0<q\le 1)$ plus an additional shear (with an arbitrary direction) as models
for the observed quadruple lenses. It is shown that a minimum additional shear
is needed even just to reproduce the observed positions alone. We also obtain
the dependence of the axial ratio, $q$, on the orientation of the major axis of
potential. A general relation also exists between the shear, the position angle
and axial ratio of the lensing galaxy. The relation shows a generic degeneracy
in modelling quadruple lenses. In particular, it shows that only the ratio of
the ellipticity, $\epsilon\equiv (1-q^2)/(1+q^2)$, to the magnitude of shear,
$\gamma$ can be determined. All these results are valid regardless of the
radial profile of the potential. Our formalism applies when the galaxy position
is observed, which is the case for seven of the eight known quadruple lenses.
Application to these seven cases reveals two quadruple lenses CLASS 1608+656
and HST 12531-2914, requiring highly significant shear with magnitude $\approx
0.2$. For HST 12531-2914, there must be a misalignment between the major axis
of light and the major axis of potential (mass). We conclude that detailed
modelling of quadruple lenses can yield valuable quantitative information about
the shape of lensing galaxies and their dark matter halos.
 ( http://xxx.lanl.gov/abs/astro-ph/9702021 ,  44kb)
\\


Paper: astro-ph/9702194
From: wozniak@astro.Princeton.EDU
Date: Fri, 21 Feb 1997 15:32:14 -0500 (EST)   (191kb)

Title: Microlensing of Blended Stellar Images
Author: Przemyslaw Wozniak, Bohdan Paczynski (Princeton University Observatory,
  USA)
Comments: 16 pages, 6 figures, Latex, aaspp4
Report-no: POP710
\\
  The current modelling of single microlensing light curves neglects the
possibility that only a fraction of the light is due to the lensed star, the
remaining being due to a close, unresolved blend, which may be related or
unrelated to the lens. Unfortunately, the effects of blending are significant
as all microlensing experiments choose very crowded fields as their targets. In
this paper we point out a strong degeneracy of the fitting procedure which
makes it practically impossible to detect the presence of a blend by purely
photometric means, except in a small part of the parameter space. Some blends
may be detected by astrometric means, but the majority have to be corrected for
statistically. The luminosity function reaching well below the ground based
detection limit (with the HST) would be very also important and this could be
determined with the repeating microlensing events. If no correction is made
then the event time scales, the lens masses, and the optical depth are all
systematically underestimated.
 ( http://xxx.lanl.gov/abs/astro-ph/9702194 ,  191kb)
\\


Paper: astro-ph/9512110
Xiang-Ping Wu wu@time.physics.arizona.edu
Date: Sun, 17 Dec 1995 14:42:45 -0700 (MST)

Title: GRAVITATIONAL LENSING IN THE UNIVERSE
Author: Xiang-Ping Wu
Comments: Latex file, 55 pages, 32 figures (not included). Fundamentals of
  Cosmic Physics, in press
\\
  This work reviews the basic theoretical aspects, the main observational
evidences and the recent applications of gravitational lensing in the Universe.
The article is aimed particularly at providing the readers who don't work on
gravitational lensing a relatively easy introduction to this active research
field in today's astrophysics. (astro-ph/9512110 ,  208kb)
\\


Paper: astro-ph/9701196
From: wxp@bao01.bao.ac.cn
Date: Sat, 25 Jan 1997 17:30:13 +0800

Title: A Statistical Comparison of Cluster Mass Estimates from Optical/X-ray
  Observations and Gravitational Lensing
Authors: Xiang-Ping Wu and Li-Zhi Fang
Comments: 18 pages plus 4 figures, using aastex. To appear in ApJ
\\
  We present a statistical comparison of three different estimates of cluster
mass, namely, the dynamical masses obtained from the velocity dispersion of
optical galaxies, the X-ray masses measured from the temperature of X-ray
emitting gas under the assumption of isothermal hydrostatic equilibrium, and
the gravitational lensing masses derived from the strong/weak distortions of
background galaxy images. Using a sample of 29 lensing clusters available in
literature, we have shown that the dynamical masses are in agreement with the
gravitational lensing masses, while the X-ray method has systematically
underestimated cluster masses by a factor 2-3 as compared with the others.
These results imply that galaxies indeed trace the gravitational potential of
their clusters, and there is no bias between the velocities of the dark matter
particles and the galaxies in clusters. The X-ray cluster mass discrepancy is
probably from the simplification in the models for the X-ray gas distribution
and dynamical evolution.
 (http://xxx.lanl.gov/abs/astro-ph/9701196 ,  22kb)
\\


Paper: astro-ph/9508146
HongSheng Zhao hsz@MPA-Garching.MPG.DE
Date: Wed, 30 Aug 1995 21:35:14 +0200

Title: A SELF-CONSISTENT DYNAMICAL MODEL FOR THE COBE OBSERVED GALACTIC BAR AND ITS APPLICATION TO MICROLENSING
Author: HongSheng Zhao
Comments: 6 pages, 2 figures, compressed and uuencoded. Contributed talk at IAU
  symposium 157, "Barred Galaxies"
\\
  A self-consistent stellar dynamical model for the Galactic bar is constructed
from about 500 numerically computed orbits with an extension of the
Schwarzschild technique. The model fits the {\sl COBE} found asymmetric boxy
light distribution and the observed stellar kinematics of the bulge. The model
potential is also consistent with the non-circular motions of the HI and CO
velocity maps of the inner Galaxy. We also use the stellar bar model to
construct a N-body model to study stability and a microlensing map towards the
bulge, which can account for the observed optical depth and the event duration
by the MACHO and OGLE collaborations. The technique used here can be applied to
interpret light and velocity data of external bulges/bars and galactic nuclei.
\\


Paper: astro-ph/9606166
From: HongSheng Zhao hsz@strw.LeidenUniv.nl
Date: Thu, 27 Jun 1996 12:39:52 +0200

Title: POSSIBLE IMPLICATIONS OF SAGITTARIUS TYPE DWARF GALAXY ON MICROLENSING TOWARDS THE LARGE MAGELLANIC CLOUDS
  Towards the Large Magellanic Cloud
Authors: HongSheng Zhao (Sterrewacht Leiden and MPA-Garching)
Comments: 3 pages in Latex, compressed uuencoded, no figure. Submitted to MNRAS
\\
  The discovery of the Sgr dwarf galaxy shows that the Galactic halo contains
large clumps which are not full viralized. This may change implications of
observed microlensing events towards the LMC. If more than one such systems are
hidden in the Galactic halo, then given their enormous angular size, there is a
significant chance for {\sl any} line of sight, say the LMC direction, to
intersect one of them. I use parameters of the Sgr dwarf galaxy to demonstrate
that a foreground dwarf galaxy can provide much more micro-lenses than an
isothermal dark halo of massive compact objects (MACHOs). As an alternative to
the half-MACHO dark halo model, I discuss a model with lenses of the observed
events being faint stars in a hidden Sgr-like disintegrated dwarf galaxy in the
line-of-sight path to the LMC.
(http://xxx.lanl.gov/abs/astro-ph/9606166 ,  7kb)
\\


Paper: astro-ph/9703097
From: HongSheng Zhao hsz@strw.LeidenUniv.nl
Date: Fri, 14 Mar 1997 19:14:35 +0100   (17kb)

Title: Microlensing of tidal debris on the Magellanic great circle
Authors: HongSheng Zhao (Leiden)
Comments: 18 pages no figure
\\
  Increasing evidences suggest that the Galactic halo is lumpy on kpc scales
due to the accretion of at least a dozen small galaxies (LMC/SMC, Sgr, Fornax
etc.). Faint stars in such lumpy structures can significant microlense a
background star with an optical depth $10^{-7}-10^{-6}$, which is comparable to
the observed value to the LMC (Alcock et al. 1996c). The observed several
microlensing events towards the LMC can be explained by a tidal debris tail
lying in the Magellanic plane if the progenitor of the Magellanic Clouds and
Stream and other satellite galaxies in the Magellanic plane has a mass about
twice that of the disc of the LMC. Two classes of models are studied: the LMC
stars can either lense stars in the debris tail behind the LMC, or be lensed by
stars in the part of debris tail in front of the LMC. The models are consistent
with an elementary particle dominated Galactic halo without massive compact
halo objects (MACHOs). They also differ from Sahu's (1994) LMC-self-lensing
model by predicting a higher optical depth and event rate and less
concentration of events to the LMC center.
 ( http://xxx.lanl.gov/abs/astro-ph/9703097 ,  17kb)
\\


Paper: astro-ph/9605030
From: HongSheng Zhao hsz@MPA-Garching.MPG.DE
Date: Wed, 8 May 1996 00:26:58 +0200

Title: ON THE MICROLENSING OPTICAL DEPTH OF THE GALACTIC BAR
Authors: HongSheng Zhao and Shude Mao (MPA-Garching)
Comments: 28 pages including 6 postscript figures in uuencoded compressed tar
  file. Submitted to MNRAS
Report-no: MPAxxx
\\
  The microlensing probability (optical depth $\tau$) toward the Galactic
center carries information about the mass distribution of the Galactic
bulge/bar, so can be used to constrain the very uncertain shape parameters of
the bar. We find $tau$ depends on the bar mass, radial profile, angle, axis
scale lengths and boxyness by a few simple analytical formulae, which shows:
(1) $\tau$ is proportional to the mass of the bar, $M$. (2) $\tau$ falls along
the minor axis with a strong gradient. (3) An oblate bulge can have more
optical depth than a triaxial bar if the bar angle $\alpha>45$ degress. (4)
$\tau$ is the largest if the angle $\alpha$ and the axis ratio $y_0/x_0$
conspires so that $y_0/x_0=\tan \alpha$. (5) At a fixed field on the minor axis
but away from the center, boxy bars with a flat density profile tend to give a
larger optical depth than ellipsoidal bars with a steep profile. (6) Main
sequence sources should have a significantly lower (20-50\% lower) optical
depth than red clump giants if main sequence stars are not observed as deep as
the bright clump giants.
  An application to four COBE-constrained models (Dwek et al. 1994) shows most
models produce optical depth $2\sigma$ lower than MACHO and OGLE observed
values even with both a massive bar $2.8\times 10^{10} M_\odot$ and a full
disk. The high $\tau$ argues for a massive ($> 2\times 10^{10}M_\odot$) boxy
bar with $y_0/x0\simeq \tan\alpha$ and $\alpha<20$ deg and with a flat radial
profile up to corotation.
(http://xxx.lanl.gov/abs/astro-ph/9605030 ,  97kb)
\\


Paper: astro-ph/9702159
From: Zong-Hong Zhu zzh@class2.bao.ac.cn
Date: Wed, 19 Feb 1997 12:35:32 +0800 (CST)   (4kb)

Title: A remark on the inversion of the magnification bias in the quasar-galaxy
  associations
Authors: Zong-Hong Zhu and Xiang-Ping Wu
Comments: 3 pages, no figure, A\&A in press
\\
  We present an alternative but intuitive method of obtaining the true or
intrinsic quasar luminosity function through the observed one in the framework
of gravitational lensing. Such a so-called inversion of the magnification bias
can be straightforwardly performed by means of the Mellin transformation
instead of other complex methods. Application of our approach to the well-known
form of the observed quasar luminosity function identifies the previous results
in literature.
 ( http://xxx.lanl.gov/abs/astro-ph/9702159 ,  4kb)
\\


%N\input endla

\end{document}
