Carbon Isotopic Abundances in the Red Giants of ω Centauri (NGC 5139)

Carbon-12 and carbon-13 abundances have been measured in eleven bright giant members of the globular cluster ω Centauri via observations of the first-overtone CO bands near 2.3 µm. The stars in this sample were selected to span a substantial fraction of the range of iron abundances found in this cluster. In addition, the sample covers a range of [O/Fe], [Na/Fe] and [Al/Fe] abundance ratios derived in previous studies. In all ω Cen giants the 12 C / 13 C abundance ratio is found to be quite low, indicating deep mixing in these red giants. The mean value for the entire sample is 〈 12 C / 13 C 〉 = 4.3 ± 0.4 (σ = 1.3), with nine stars equal, within the errors, to the equilibrium ratio