The unusual abundance of copper in the Sagittarius dwarf spheroidal galaxy and implications for the origin of omega Centauri

We present copper abundances for 14 red giant stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph), showing that [Cu/Fe] is deficient by similar to 0.5 dex, relative to the Galactic trend. This is most easily understood as due to an enhanced contribution of iron peak nucleosynthesis products from Type Ia supernovae (SNe Ia). The deficient [Cu/Fe] ratios might also be the result of a metallicity-dependent yield from SNe Ia, similar to previous conclusions for Mn, although SN Ia nucleosynthesis predictions suggest a negligible Cu yield. The enhanced SN Ia products, suggested by our low [Cu/Fe] ratios, fit a leaky box chemical evolution scenario for the Sgr dSph, where ejecta from the old, metal-poor, population overwhelmed nucleosynthesis products from younger generations, resulting in young stars with uncharacteristic compositions. The only other system known to have unusually low [Cu/Fe] is the Galactic globular cluster omega Cen, which, like the Sagittarius dwarf galaxy, has strong enhancements of s-process elements. Thus, our copper abundances lend support to the idea that omega Cen is the remaining nucleus of an accreted dwarf galaxy.