Infrared-luminous giants in 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).