The composition of the Sagittarius dwarf spheroidal galaxy and implications for nucleosynthesis and chemical evolution

We have measured the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using high S/N Keck HIRES echelle spectra. For the Sgr dSph stars with [Fe/H]>=-1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the a-elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the odd-numbered iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old, metal-poor population, including products of AGB stars and type Ia supernovae (SN).