AAS 201st Meeting, January, 2003
Session 80. Gravitational Lenses
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[80.05] MEGA: Microlensing and Variable Stars in M31

D.R. Alves, A. Bergier, A.P.S. Crotts, P. Cseresnjes, A. Gersch (Columbia), MEGA Collaboration

The nature of dark matter in spiral galaxy halos is unknown. Microlensing surveys like MACHO may have detected massive compact objects in our own Galactic dark halo. In fact these halo objects may account for as much mass as the entire Galactic disk. A controversial result like MACHO's would be strongly reinforced if similar objects were found in other spiral galaxy dark halos. The existence of compact dark halo objects would also have greater relevance to theories of galaxy formation. M31 is the best nearby spiral galaxy to survey for microlensing. It is particularly well suited to mapping out the spatial distribution of microlensing events, which can indicate whether the lenses are located in M31's halo.

MEGA is a next generation microlensing and variable star survey of M31. We have collected over a terabyte of wide-field CCD images from telescopes at KPNO, MDM, INT, Subaru, and CFHT in the past 5 years, and observations are ongoing. We will present preliminary results from our image subtraction analysis of these data. Variable star science with the MEGA survey will also be discussed. For example, we have discovered tens of thousands of new variable stars in M31, including some in globular clusters (GCs). Many types of rare and important variable stars found in Milky Way GCs have yet to be discovered in M31 GCs.

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