Wide Field Imaging of the Sextans Dwarf Spheroidal Galaxy

Abstract

We present wide field multiband photometry of the very low surface brightness dwarf Spheroidal galaxy (dSph) Sextans. We have found convincing evidence for the presence of multiple stellar populations in this galaxy. In particular we discovered: (a) a Blue Horizontal Branch tail kinked over the instability strip; (b) a clearly bimodal distribution in color of the Red Giant Branch (RGB) stars and (c) a double RGB-bump. All these features suggest that (at least) two components are present in the old stellar population that dominates the galaxy: a main one with [Fe/H]~-1.8 and a minor component around [Fe/H]~-2.5. Similar evidence has been recently found by Majewski et al. (1999) for the Sculptor dwarf Spheroidal, suggesting that multiple star formation episodes are common also in the most nearby dSphs that ceased their star formation activity at very early epochs.

4 pages, 2 figures, poster paper to appear in the Coimbra 2001 Colloquium proceedings on "Observed HR diagrams and stellar evolution"