PHOTOMETRIC VARIABILITY AMONG THE BRIGHTEST ASYMPTOTIC GIANT BRANCH STARS NEAR THE CENTER OF M32

摘要

Deep K′ images with 0.1″ angular resolution, obtained with Altair+NIRI on Gemini North, are used to investigate photometric variability among the brightest asymptotic giant branch (AGB) stars in the central regions of M32. On the basis of a comparison with brightnesses obtained from the K-band data discussed by Davidge et al., it is concluded that (1) at least 60% of bright AGB stars near the center of M32 are photometrically variable, and (2) the amplitudes of the light variations are similar to those of long-period variables in the Galactic bulge. We do not find evidence for a population of large-amplitude variables, such as those detected by IRAS in the Galactic bulge. The technique discussed here may prove useful for conducting an initial reconnaisance of photometric variability among AGB stars in spheroids in the Virgo Cluster and beyond, where the required long exposure times may restrict observations to only a few epochs.