Isotopic Carbon Ratios Among M71 Bright Red Giants
Session 74 -- Globular Clusters
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [74.12] Isotopic Carbon Ratios Among M71 Bright Red Giants

M. M. Briley, V. V. Smith (U. Texas)

We present high signal-to-noise, high resolution spectra of 8000 \AA ${}^{12}CN$ and ${}^{13}CN$ bands in two pairs of CN strong/weak M71 (C1951+186, NGC 6838) bright giants. The program stars were chosen from the recent survey of Sneden et al. 1993 (AJ, submitted) for their differing $[O/Fe]$ 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 among other cluster stars (e.g. M92, M15, M13, M3, and M5, Sneden et al. 1991, AJ, 102, 2001; Sneden et al. 1992, AJ, 104, 2121; Kraft et al. 1992, AJ, 104, 645; and Drake et al. 1992, ApJL, 395, L95), have been suggested to be the result of differing degrees of deep-mixing (Langer et al. 1993, PASP 105, 301). Our analysis of the present observations with synthetic spectra yields a ${}^{12}C/^{13}C$ ratio of about $7 \pm 1$ for all four stars, regardless of CN band strength, $[O/Fe]$, and $[Na/Fe]$. This implies that while these stars have undergone extensive mixing of at least CN-processed material to the stellar surface, there is little star-to-star difference in the extent of the dredge-up and the observed abundance patterns may not be entirely due to mixing.