Annu. Rev. Astron. Astrophys. 1989. 27: 139-59
Copyright © 1989 by . All rights reserved

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5.6 M32

Because of its brightness and its proximity, a great deal of work has been done on the elliptical galaxy M32, also a companion to M31, going back to the early work of Stebbins & Whitford (117) and even before. It has recently been studied by Faber (41), Pritchet (100), Frogel et al. (47), Wu et al. (133), O'Connell (97), Gunn et al. (54), Burstein et al. (21), Rose (104), and others. All agree that M32 is not just an overluminous globular cluster in its stellar population. Both from spectrophotometry and from integrated colors, it clearly differs from Galactic globular clusters, either metal poor or metal rich. Although at long wavelengths M32 matches 10-15-Gyr-old metal-rich globular clusters, at short wavelengths it is distinctly different, both in its excess blue light and in its line strengths. It is not easy to distinguish between the effects of (a) a small number of young stars, (b) an anomalously large population of blue stragglers, (c) a shorter global age, (d) a strong metal-poor component, or (e) a significant population of intermediate-age stars. The extensive analyses of O'Connell (97) and Rose (104) both argue convincingly for the last of these. Rose (104), for example, finds that most of the light at 4000 Å comes from slightly metal-poor dwarf stars of intermediate age. Thus, although there is a metal-poor old population (contributing perhaps 10% of the light at blue wavelengths), many stars were forming as recently as 10 Gyr ago, though very little star formation has occurred more recently.