Abundances of Baade’s Window Giants from Keck HIRES Spectra. I. Stellar Parameters and [Fe/H] Values

Abstract

We present the first results of a new abundance survey of the Milky Way bulge based on Keck HIRES spectra of 27 K giants in the Baade's Window (l=1deg, b=-4deg) field. The spectral data used in this study are of much higher resolution and signal-to-noise ratio than previous optical studies of Galactic bulge stars. The [Fe/H] values of our stars, which range between -1.29 and +0.51, were used to recalibrate large low-resolution surveys of bulge stars. Our best value for the mean [Fe/H] of the bulge is -0.10+/-0.04. This mean value is similar to the mean metallicity of the local disk and indicates that there cannot be a strong metallicity gradient inside the solar circle. The metallicity distribution of stars confirms that the bulge does not suffer from the so-called G dwarf problem. This paper also details the new abundance techniques necessary to analyze very metal-rich K giants, including a new Fe line list and regions of low blanketing for continuum identification. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.