AAS 201st Meeting, January, 2003
Session 14. Galaxy - Contents
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[14.14] Keck Spectroscopy of Red Giants in the M31 dSph Satellites: Chemical Abundance Spread

S. Datta (UCO Lick Obs, UCSC), L. Pittroff (MPI for Extraterrestrial Physics, Germany), P. Guhathakurta (UCO/Lick Obs, UCSC), E. Grebel, D. Harbeck (MPI for Astronomy, Germany)

Dwarf spheroidals (dSphs), the smallest variety of dwarf galaxies, are important ``building blocks'' in the process of galaxy formation and evolution. As part of a broader survey of the physical properties of Local Group dwarf galaxies, we present a study of the intrinsic chemical abundance spread in four M31 dSphs, And I, And III, And V, and And VI (Peg dSph). This study is based on multi-slit spectroscopy of about 100 red giants with the Keck 10-meter telescope and Low Resolution Imaging Spectrometer (LRIS) and color-magnitude diagrams (CMDs) derived from archival Hubble Space Telescope WFPC2 and LRIS imaging data. For each star, spectroscopic estimates of the metallicity [Fe/H] on the Zinn & West (1984) and Carretta & Gratton (1997) scales, derived from the absorption line strength of the near-infrared Ca II triplet, are compared to photometric estimates of [Fe/H] derived from the CMDs; both spectroscopic and photometric [Fe/H] estimates are based on empirical calibration relations derived from Galactic globular cluster data. The different [Fe/H] estimates for member stars in each dSph appear to be correlated, indicating a spread of about 1 dex for And I and And VI and about 0.5 dex for And III and And V. Our results suggest a complex chemical enrichment history, likely as a result of multiple epochs of star formation, similar to what has been observed in their Galactic counterparts. This degree of complexity is surprising given the low mass/shallow gravitational potential well of these dSphs. A dynamical analysis of the same LRIS data is presented in a companion poster by Pittroff et al..

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