Abundances of Red Giants in the Andromeda II Dwarf Spheroidal Galaxy

We have obtained spectra for 50 candidate red giants in Andromeda II (a dwarfspheroidal companion of M31) using LRIS on the Keck II telescope. Aftereliminating background galaxies and Galactic foreground stars, we are left witha sample of 42 red giants for which membership in Andromeda II can beestablished unambiguously from radial velocities. Line indices measured on theLick/IDS system are combined with V and I photometry obtained with the Keck IIand Palomar 5m telescopes to investigate the age and metallicity distributionof these stars. Based on a comparison of the measured line indices to those ofLick/IDS standard stars in globular and open clusters, we derive a meanmetallicity of [Fe/H] = -1.47+/-0.19 dex. This confirms earlier conclusionsbased on Thuan-Gunn gr photometry that Andromeda II obeys the familiar relationbetween mean stellar metallicity and galaxy luminosity. There is also evidencefor a dispersion in metallicity of 0.35+/-0.10 dex based on the scatter in themeasured Mgb line indices and the observed width of the galaxy's giant branch.Although existing observations of Local Group dwarf galaxies indicate thattheir mean stellar metallicity depends rather sensitively on host galaxyabsolute magnitude, the internal spread in metallicity appears to be relativelyindependent of luminosity. Finally, a small number of stars are found above thePopulation II red giant branch, indicating the presence of a modestintermediate-age population in this galaxy. (ABRIDGED).Comment: 23 pages, 14 postscript figures. Accepted for publication in the Astronomical Journa