K Giants in Baade's Window. II. The Abundance Distribution

Abstract

This is the second in a series of papers in which we analyze spectra of over 400 K and M giants in Baade's Window, including most of the stars with proper motions measured by Spaenhauer et al. [AJ, 103, 297 (1992)]. In our first paper, we measured line--strength indices of Fe, Mg, CN and H$β$ and calibrated them on the system of Faber et al. [ApJS, 57, 711 (1985)]. Here, we use the $\langle{\rm Fe}\rangle$ index to derive an abundance distribution in [Fe/H] for 322 stars with effective temperatures between 3900 K and 5160 K. Our derived values of [Fe/H] agree well with those measured from high--resolution echelle spectra (e.g., McWilliam \& Rich [ApJS, 91, 749 (1994)]) for the small number of stars in common. We find a mean abundance $\langle{\rm [Fe/H]}\rangle = -0.11 \pm 0.04$ for our sample of Baade's Window K giants. More than half the sample lie in the range $-0.4 <$ \feh\ $<+0.3$. We estimate line--of--sight distances for individual stars in our sample and confirm that, in Baade's Window, most K giants with $V < 15.5$ are foreground disk stars, but the great majority (more than 80\%) with $V > 16$ belong to the bulge. We also compare the metallicities derived from the CN and Mg$_2$ indices to those from iron. Most of the metal--rich stars in our sample appear to be CN--weak, in contrast to the situation in metal--rich globular clusters and elliptical galaxies. The metal--poor half of our sample ([Fe/H] $< 0$) shows evidence for a mild Mg overenhancement ([Mg/Fe] $\sim +0.2$); but this is not seen in the more metal--rich stars ([Fe/H] $\geq$ 0). The K giants in Baade's Window therefore share some, but not all, of the characteristics of stars in elliptical galaxies as inferred from their integrated light.

Accepted for publication in the Astronomical Journal, tentatively scheduled for July, 1996. LaTex source which generates 40 pages of text (no figures or tables). Complete (text + 15 figs + 5 tables) preprint in gzip/tar format is also available at ftp://bessel.mps.ohio-state.edu/pub/terndrup/kg2.tar.gz (227 kbyte)