2002ApJ...579..832S

¹²C and ¹³C abundances have been measured in 11 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 ¹²C/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 <¹²C/¹³C≥4.3±0.4 (σ=1.3), with nine stars equal, within the errors, to the equilibrium ratio ¹²C/¹³C=3.5 and two stars having slightly higher values. There is no correlation between the ¹²C/¹³ C and the abundance of iron. In addition, no correlation of ¹²C/¹³C with [¹²C/Fe] is found (all giants are deeply mixed), although the derived abundances of [¹²C/Fe] show a positive correlation with [O/Fe] and an anticorrelation with [Na/Fe] (with the oxygen and sodium abundances taken from previous studies in the literature). A comparison of the isotopic carbon ratios in ω Cen with those from other globular clusters (M4, M71, NGC 6752, and 47 Tuc) and with literature oxygen abundances, may reveal a slight trend of decreasing ¹²C/¹³C ratios with decreasing [O/Fe] in the entire globular cluster sample of red giants. A comparison between ¹²C/¹³C and both [Na/Fe] and [Al/Fe], however, reveals no trend.