Assigned ID: 65 ----- Attempting Submission 1 (Tue Feb 23 19:22:53 GMT 2010) ----- We propose to reduce and analyze WFPC2 and ACS/WFC imaging of 7 fields in the Andromeda galaxy (M31) and its environs in order to characterize its variable star content. We will likely isolate a variety of different types of variable stars including Cepheids and RR Lyraes. The presence of RR Lyrae variables suggests the presence of an old (Age >~ 10 Gyr) stellar population. In addition, because the minimum-light color of ab-type RR Lyraes is a constant irrespective of metallicity or period, these stars can be used to study the extinction along the line of sight. Furthermore, the period of ab-type RR Lyraes is directly related to their metal abundance so that we can also study the metallicity distribution function of different regions of M31 as well its radial metallicity gradient. We will also determine the slope of the RR Lyrae luminosity - metallicity relation.

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