Name: Andreas Koch
Institution: Astronomical Institute of the Univ. of Basel
University of Washington
Astrolunch
Title: Chemical Evolution in the Carina dSph
Abstract:
Numerous photometric analyses of the faint Carina dwarf spheroidal (dSph) galaxy have revealed that it contains an
intriguing variety of distinct stellar populations, showing both a prominent old and an intermediate population as
well as a younger population not older than 3 Gyr. This implies that Carina must have undergone several star forming
(SF) episodes with at least three significant maxima.
Here we present the metallicity distribution for 487 red giant stars in Carina from medium- resolution spectroscopy
of the calcium triplet that was obtained in the framework of a VLT Large Programme using the FLAMES multiobject
instrument. Exploiting the instrument's large field of view and high multiplexing capability, this programme was
designed to extend our chemical and kinematical analyses into several fields, well out to the tidal radius at 30'
from the galaxy's center. This data sample is the largest compilation to date of spectroscopically derived
metallicities for a Local Group dSph. We find a mean [Fe/H] of -1.9 dex, with a full spread in metallicities of at
least one dex. Such a large range in [Fe/H], combined with an age-metallicity relation over the extended periods of
SF previously inferred from the color-magnitude diagram, is able to provide the observed narrow width of Carina's
red giant branch (e.g., Smecker-Hane et al. 1999). We find a mild dependence of metallicity on radial location, in
that the more metal poor stars preferentially reside in the outer regions of the Carina dSph. These results are
compared with different evolutionary models and are discussed in the context of the SF history and chemical
evolution of the Carina dwarf galaxy.
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