CNO Abundances in Metal-Poor Stars

Carbon, nitrogen, and oxygen produced in the early universe come from a variety of possible astrophysical sites. Among these are early supernovae, winds of massive, rapidly-rotating, mega metal-poor stars, and intermediate mass AGB stars. Large-scale surveys such as the HK Survey of Beers and colleagues and the Hamburg/ESO Survey of Christlieb and colleagues have allowed for the identification of numerous metal-poor stars in the Galactic halo. Follow-up observations of these metal-poor stars is necessary to determine CNO abundances. Techniques have been developed such that [C/Fe], [N/Fe], and [O/Fe] can be estimated with considerable accuracy using medium-resolution observations alone. We present estimates of these species for a number of metal-poor stars based on analysis of near-UV, optical, and near-IR spectra. The data come from several different instruments on southern-hemisphere telescopes, including the Goodman HTS and OSIRIS on SOAR, GMOS-S on Gemini, and XSHOOTER on VLT. In this way, we present some of the first metal-poor stars with a full complement of CNO abundances based solely on the analysis of medium-resolution spectra.