AAS 195th Meeting, January 2000
Session 48. Lensing
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[48.02] The MACHO Project: Microlensing Results from 5.7 Years of LMC Observations

A.C. Becker (U.Washington), C. Alcock (LLNL), R.A. Allsman (ANUSF), D. Alves (STSCI), T.S. Axelrod (MSSSO), D.P. Bennett (Notre Dame), K.H. Cook (LLNL), A.J. Drake, K.C. Freeman (MSSSO), M. Geha (LLNL), K. Griest (UCSD), M.J. Lehner (Sheffield), S.L. Marshall (LLNL), D. Minniti (P. Universidad Catolica), C.A. Nelson (LLNL), B.A. Peterson (MSSSO), P. Popowski (LLNL), M.R. Pratt (Washington), P.J. Quinn (Notre Dame), A.W. Rodgers (), C.W. Stubbs (Washington), W. Sutherland (Oxford), A.B. Tomaney (Washington), T. Vandehei (UCSD), D.L. Welch (McMaster), MACHO Collaboration

We report on our search for microlensing towards the Large Magellanic Cloud (LMC). Analysis of 5.7 years of photometry on 11.9 million stars in the LMC reveals 17 candidate microlensing events. A careful treatment of our detection efficiency shows that this is significantly more than the ~ 2 to 4 events expected from lensing by known stellar populations. The timescales ({\widehat t}\,) of the events range from 34 to 230 days. The spatial distribution of events is probably inconsistent with LMC/LMC disk self-lensing, but consistent with an extended lens distribution such as a Milky Way or LMC halo.

The optical depth results appear consistent with, but are lower than, our previous 2.1 year results. Besides a factor of 3.4 increase in exposure, this new work also includes an improved efficiency determination, improved likelihood analysis, and more thorough testing of robustness and systematic errors, especially in regards to the treatment of potential backgrounds to microlensing, such as supernovae in galaxies behind the LMC.

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