ABUNDANCES FOR GIANT STARS IN THE DRACO DWARF GALAXY

We have determined the abundances of 14 giant stars with +0.2 > M(V) > -2.5 (19.6 > V > 16.9) in the Draco dwarf galaxy, using a synthetic spectral analysis of the calcium infrared triplet and the strongest line (5183 angstrom) of the magnesium b triplet. The average abundance of the galaxy is approximately -1.9 +/- 0.4 (all quoted uncertainties are 1-sigma), with a range from approximately -1.4 to -2.4. As previously noted by Zinn and Kinman et al., the abundances seem to fall into two groups, one with an average [Ca, Mg/H] near -1.6 +/- 0.2 and the other -2.3 +/- 0.2. These results confirm and, in two significant ways, extend other claims for an abundance spread. First, our study "tends to stars about 1.5 mag fainter than previous spectroscopic studies and is thus less sensitive to uncertainties arising from rapid evolutionary or mixing processes near the peak luminosity of the red giant branch and asymptotic giant branch, or from modeling quite extended atmospheres. Second, our study is one of the few to use model atmosphere techniques to match absorption features. A discussion of the origin of the color range among Draco giants and other problems of understanding dwarf spheroidal galaxy formation and evolution is presented.