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J. Van Duyne, A. Sarajedini (Wesleyan University)
We present a photometric analysis of the outer disk of M31 based on archival images from the Hubble Space Telescope. The reduction of these data produces an I vs. V-I color-magnitude diagram that extends well below the red clump down to magnitudes possibly approaching the turn-off point of the population.
The primary goal of this study is to examine the metallicity range in the outer disk of M31. We shall accomplish this by examining the color width of the red giant branch (RGB). Since a significant portion of this width is due to photometric error, principally caused by the prodigious crowding in these frames, we have performed artificial star experiments to quantify these errors and account for this effect. A secondary goal of this work is to construct luminosity functions of the disk in order to further study its stellar populations. Analysis of the metallicity will be performed through a comparison of the M31 disk RGB with those of Milky Way globular clusters with well-determined metallicities, such as M15 and 47 Tuc, among others.