ISOTOPIC CARBON RATIOS AMONG M71 BRIGHT RED GIANTS

We present high signal-to-noise, high-resolution spectra of 8005 angstrom (CN)-C-12 and (CN)-C-13 lines in two groups of CN strong/weak M71 (C1951 + 186, NGC 6838) bright giants chosen for their different [O/Fe] and [Na/Fe] abundances, as well as CN band strengths. These abundance variations in M71, as well as similar star-to-star differences in [O/Fe] and [Na/Fe] seen in other clusters (e.g., M92, M15, M13, M3, and M5), have been suggested to result from differing degrees of deep mixing. Our analysis of the present observations with synthetic spectra yields C-12/C-13 ratios ranging from 4.9 to 8.9; the CN-strong/O-poor stars exhibit slightly lower ratios. This C-12/C-13 difference between. the two groups may conceivably be the result of differing degrees of the dredge-up.