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 degrees, -1 degrees), based on infrared spectroscopy (1.5-1.8 mu m) using NIRSPEC at the Keck telescope. Based on their R p 25,000 luminosities and radial velocities, we identify these stars with a stellar population older than 1 Gyr. We find the iron abundance <[Fe/H]> = -0.22 +/- 0.003, with a 1 sigma dispersion of 0.14 +/- 0.024. We also find the bulge stars have an enhanced [alpha/Fe] abundance ratio at the level of +0.3 dex relative to solar stars, and low < C-12/C-13 > approximate to 6.5 +/- 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.