The MACHO Project IV: Variable Stars in the Large Magellanic Cloud

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Session 84 -- Variable Stars
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[84.01] The MACHO Project IV: Variable Stars in the Large Magellanic Cloud

C. Alcock, R. Allsman, T. Axelrod, K. Cook, H.-S. Park (LLNL), K. Freeman, B. Peterson, P. Quinn, A. Rodgers (MSSSO), C. Akerlof, D. Bennett, K. Griest, S. Marshall, S. Perlmutter, M. Pratt, J. Reimann, C. Stubbs, W. Sutherland (CfPA)

The MACHO Project database contains lightcurves for six million stars, with (typically) ~300 photometric measurements. Preliminary to searching for the photometric variation characteristic of gravitational microlens amplification, the lightcurve for each star is examined for possible intrinsic variation in the star itself. This procedure yields lists of stars which exhibit photometric variation exceeding that expected from the photometric errors. These lightcurves are tested for periodic variation using a non-parametric least squares fitting program. We have found that the majority of stars identified as candidates for intrinsic variability are periodic variables, and further that periods as short as a few hours can reliably be identified. The resulting catalog of periodic variables comprises principally Cepheid variables, RR Lyrae stars, and eclipsing binary main sequence stars.

In addition to the known categories of periodic variable stars, there are aperiodic objects, most of which are probably asymptotic giant branch stars, and some possibly new types of variable stars. We recorded Nova LMC 1992. Some of the aperiodically variable objects may turn out to be quasars; we discuss the possibility for using this database to find quasars behind the LMC.

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