2005AJ....129..201D

Deep J, H, and K' images, recorded with the ALTAIR adaptive optics system and NIRI imager on Gemini North, are used to probe the stellar content of the disk and bulge of the Local Group galaxy M31. With an FWHM near 0".08 in K, these are the highest angular resolution near-infrared images yet obtained of this galaxy. One field samples the outer disk of M31 at a galactocentric distance of roughly 62' along the major axis. The mean metallicity in this field is close to that of the metal-rich globular cluster NGC 6528, and no stars with [Fe/H]←0.7 are detected. Another field, located on the major axis 9' from the galaxy center, contains a roughly equal mix of disk and bulge stars. The red giant branch (RGB) in this field is redder than that of NGC 6528, although it is argued that reddening internal to M31 may be significant in this region of the galaxy. The remaining two fields, located at projected galactocentric distances of 2' and 4', are dominated by bulge stars. The RGB tip occurs between K=17.0 and 17.2, and the color of the RGB in the field closest to the center of M31 is consistent with that of NGC 6528. After accounting for random photometric errors, the upper RGB in each field has a width on the (K, J-K) color-magnitude diagrams that is consistent with a ±0.5 dex dispersion in [Fe/H], in rough agreement with what is seen in other disk and spheroid fields in M31. The number of bright asymptotic giant branch (AGB) and RGB stars also scales with the r-band surface brightness in all four fields. Thus, we conclude that the stellar content does not change markedly from field to field and that the photometric properties of the brightest AGB stars in the two innermost fields are not affected significantly by crowding. The brightest star has M_K=-8.6 and M_bol=-5.2, although this may not be a reliable measure of the AGB-tip brightness because of photometric variability. A population of very bright red stars, which we identify as C stars, are seen in the three fields that are closest to the center of M31. The spatial distribution of these objects suggest that they are well mixed throughout this part of M31, and thus they likely did not form in a compact region near the galactic nucleus but more probably in the inner disk. We speculate that these C stars may be the most luminous members of the intermediate-age population that has been detected previously in studies of the integrated spectrum of the central regions of M31.