The age-metallicity degeneracy in the dwarf spheroidal Carina as seen by FLAMES

The Carina dwarf spheroidal galaxy is the only one of this type to show clearly episodic star formation separated by long pauses. Still its Red Giant Branch is remarkably narrow. Our medium-resolution spectroscopy of 437 Red Giants in this galactic satellite with FLAMES reveals a full range of metallicities from ~ –3.0 up to ~ 0.0 dex. There also appears to be a mild radial gradient in that more metal-rich populations are more centrally concentrated, matching a similar trend in ages with an increasing fraction of intermediate-age stars in the centre (Harbeck et al. 2001). Complemented by the colours of the more metal-rich stars, this suggests that Carina exhibits an age-metallicity relation. We address the star formation in this intriguing galaxy by also pursuing its agemetallicity degeneracy, resulting in a narrow Red Giant Branch despite the considerable spread in metallicity and wide range of ages, and applying basic models of chemical evolution