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Description
A previously unknown population of very luminous, red, asymptotic-giant-branch stars has been identified as a result of near-infrared (JHK) imaging in the dwarf elliptical galaxy M32. Situated above the tip of the normal first red giant branch, these stars are intrinsically brighter than the most luminous normal giants in old Galactic globular clusters by approximately 2 bolometric magnitudes. Moreover, they are a full bolometric magnitude brighter than the brightest giants observed in our own Galactic bulge. Several possible explanations for this population are examined, including old long-period variables, binary mergers, supermetallicity, and intermediate-age stars. It is suggested that the simplest explanation at present, is that M32 had a star formation episode less than about 5 billion years ago. These stars would then be the evolved extended asymptotic giant branch population resulting from that event (similar to those stars observed in the intermediate-age clusters in the Magellanic Clouds). This population may be similar to that in the M31 bulge, recently observed by Rich and Mould. The detection of a young component in M32 is of particular interest because historically, M32 has been a fiducial galaxy for population synthesis techniques. An understanding of M32 remains crucial for our understanding of distant and more luminous elliptical galaxies.
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