Detailed Abundances for M Giants in Two Inner Bulge Fields From Infrared Spectroscopy

We report abundance analysis for 30 M giant stars in two inner Galactic bulge fields at ( l , b ) = (0°, −1 75) and at ( l , b ) = (1°, −2 65), based on R = 25,000 infrared spectroscopy (1.5–1.8 μm) using NIRSPEC at the Keck II telescope. We find iron abundances of 〈[Fe/H]〉 = -0.16 ± 0.03 dex with a 1σ dispersion of 0.12 ± 0.02 and 〈[Fe/H]〉 = -0.21 ± 0.02 dex, with a 1σ dispersion of 0.09 ± 0.016 for the ( l , b ) = (0°, −1 75) and ( l , b ) = (1°, −2 65) fields, respectively. In agreement with all prior studies, we find enhanced [α/Fe] of +0.3 dex. We confirm the lack of any major vertical abundance or composition gradient in the innermost ∼600 pc between Baade's Window, at ( l , b ) = (1°, −3 9), and ∼150 pc from the Galactic plane. We also confirm that the known enhancement of alpha elements observed between 500 and 1000 pc from the nucleus is also present over the volume of the inner bulge and may therefore be presumed to be characteristic of all bulge/bar stars within 1 kpc of the Galactic center.