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

Abstract

We report the first abundance analysis of 17 M giant stars in the inner Galactic bulge at $(l,b)=(0°,-1°)$, 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 $<[Fe/H]>=-0.22\pm 0.03$, with a $1\sigma$ dispersion of $0.14\pm 0.024$. We also find the bulge stars have enhanced [$\mathrm{alpha}$/Fe] abundance ratio at the level of +0.3 dex relative to the Solar stars, and low ${<}^{12}\mathrm{C}{/}^{13}\mathrm{C}>\approx 6.5\pm 0.3$. 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.

Accpeted for publication in the Astrophysical Journal Letters

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