The First Detailed Abundances for M giants in the inner Bulge from Infrared Spectroscopy

We report the first abundance analysis of 17 M giant stars in the inner Galactic bulge at $(l,b)=(0\mathrm{deg},-1\mathrm{deg})$, based on $R=25,000$ infrared spectroscopy $(1.5-1.8\mu \mathrm{m})$ using NIRSPEC at the Keck telescope. Based on their luminosities and radial velocities, we identify these stars with a stellar population older than 1 Gyr. We find the iron abundance $\rm < [Fe/H] > = -0.22 \pm 0.03$,witha$1\sigma$dispersionof$0.14\pm 0.024$. We also find the bulge stars have enhanced [$\mathrm{a}\mathrm{l}\mathrm{p}\mathrm{h}\mathrm{a}$/Fe] abundance ratio at the level of +0.3 dex relative to the Solar stars, and low $\rm <^{12}C/^{13}C>\approx 6.5\pm 0.3$. The derived iron abundance and composition for this inner bulge sample is indistinguishable from that of a sample of M giants our team has previously studied in Baade’s Window $(l,b)=(0.9,-4)$. We find no evidence of any major iron abundance or abundance ratio gradient between this inner field and Baade’s window.