The First Detailed Abundances for M giants in Baade’s Window from Infrared Spectroscopy

We report the first abundance analysis of 14 M giant stars in the Galactic bulge, based on R = 25, 000 infrared spectroscopy (1.5−1.8 μm) using NIRSPEC at the Keck telescope. Because some of the bulge M giants reach high luminosities and have very late spectral type, it has been suggested that they are the progeny of only the most metal rich bulge stars, or possibly members of a younger bulge population. We find the iron abundance and composition of the M giants are similar to those of the K giants that have abundances determined from optical high resolution spectroscopy: 〈[Fe/H]〉 = −0.190 ± 0.020, with a 1σ dispersion of 0.080 ± 0.015. Comparing our bulge M giants to a control sample of local disk M giants in the solar vicinity, we find the bulge stars are enhanced in alphaelements at the level of +0.3 dex relative the Solar composition stars, consistent with other studies of bulge globular clusters and field stars. This small sample shows no dependence of spectral type on metallicity, nor is there any indication that the M giants are the evolved members of a subset of the bulge population endowed with special characteristics such as relative youth or high metallicity. We also find low C/C ≤ 10, confirming the presence of extra-mixing processes during the red giant phase of evolution. 1 Data presented herein were obtained at the W.M.Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.