Stellar Populations in the Outer Reaches of M31 and M32 from WFPC2 Photometry

Abstract

ABSTRACT Hubble Space Telescope Wide Field Planetary Camera 2 photometry in a field 7 effective radii from the nucleus of M32 and a comparison field in the outer disk of M31, already examined for the presence of RR Lyrae variable stars, are further compared. No relative distance difference between the two fields could be measured using the luminosity of red clump stars. Since M32 is projected on the half of the M31 disk inclined away from us, we argue that M32 most likely lies beyond M31. The color‐magnitude diagrams of the two fields are similar and yield abundance distributions that are similar, with the exception that M32 appears to have a narrower abundance distribution than the comparison field in M31. This conclusion is unlikely to be compromised by age effects. M32 has far fewer metal‐poor stars than the simple one‐zone model of chemical evolution predicts. The deepest combined image shows no trace of a main sequence younger than about 1 Gyr. CR - Copyright © 2004 The University of Chicago Press