Program: GS-2008A-Q-74

Elemental abundances derived using high-resolution spectra from individual stars in nearby galaxies can be used to study chemical evolution in galactic environments that are quite distinct from that of the Milky Way. The Sagittarius dwarf galaxy is particularly interesting because it is in a slow process of merging with the Milky Way. We propose to use Phoenix and Gemini-S to observe a sample of low-metallicity red-giants, with [Fe/H] ranging from -1.7 to -1.2, in order to study chemical evolution and star formation history in this dwarf galaxy. This low metallicity regime in Sgr has been essentially unexplored in high-resolution abundances studies published to date. A number of elements will be probed using IR spectroscopy, including C, N, O, F, Na, Ti, Fe and Ni. These elements trace different nucleosynthetic processes and will provide insights into the nature of chemical evolution and star formation history in this dwarf galaxy. For example, the combination of O and Na abundances, measured relative to Fe, can be used to trace both star formation efficiency, via [O/Fe], as well as inferring the relative contributions from supernovae of Type II (SN II) of different metallicities, due to the strong metallicity dependence of Na/O production. This will be the first study to follow the [O/Fe] versus [Fe/H] trend at the lowest metallicities in Sagittarius.