MANGANESE ABUNDANCES IN THE GLOBULAR CLUSTER ω CENTAURI

Abstract

We present manganese abundances in 10 red-giant members of the globular cluster Omega Centauri; 8 stars are from the most metal-poor population (RGB MP and RGB MInt1) while two targets are members of the more metal rich groups (RGB MInt2 and MInt3). This is the first time Mn abundances have been studied in this peculiar stellar system. The LTE values of [Mn/Fe] in Omega Cen overlap those of Milky Way stars in the metal poor Omega Cen populations ([Fe/H] ~ -1.5 to -1.8), however unlike what is observed in Milky Way halo and disk stars, [Mn/Fe] declines in the two more metal-rich RGB MInt2 and MInt3 targets. Non-LTE calculations were carried out in order to derive corrections to the LTE Mn abundances. The non-LTE results for Omega Cen in comparison with the non-LTE [Mn/Fe] versus [Fe/H] trend obtained for the Milky Way confirm and strengthen the conclusion that the manganese behavior in Omega Cen is distinct. These results suggest that low-metallicity supernovae (with metallicities < -2) of either Type II or Type Ia dominated the enrichment of the more metal-rich stars in Omega Cen. The dominance of low-metallicity stars in the chemical evolution of Omega Cen has been noted previously in the s-process elements where enrichment from metal-poor AGB stars is indicated. In addition, copper, which also has metallicity dependent yields, exhibits lower values of [Cu/Fe] in the RGB MInt2 and MInt3 Omega Cen populations.