Abundances in globular cluster red giants. IV - M22 and Omega Centauri

Abstract

A detailed abundance analysis has been performed using high-dispersion echelle spectra for three members of M22 and five giants in Omega Cen. The three stars in M22 are chemically identical, except for sodium, and less definitely, for barium. There is a range of 0.8 dex in the derived Na abundance of these stars, far larger than that allowed by the errors. The Omega Cen giants show that a range of chemical composition exists for all elements in this unique cluster. However, as one compares metal-poor with metal-rich stars in Omega Cen, each element is not enhanced by a constant factor. In the more metal-rich Omega Cen giants, the light elements Na, Mg, Al, Si, Ca, and Sc are all enhanced by a factor of 1.8; Ba and the rare earths are enhanced by a factor of 10. Furthermore, the two most metal-rich Omega Cen stars studied have vastly different Na, Mg, Al, and Sc abundances.