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M.M. Briley (U Wisc. Oshkosh), G.H. Smith (UCO/Lick/UCSC), C.F. Claver (NOAO)
We report V, B, and DDO C(4142) and C(4245) colors for 120 giants spanning 12 < V < 16 in the globular cluster M71. The colors were obtained from CCD images of the cluster obtained with the KPNO 0.9-m telescope. The program stars show a significant spread in C(4142) colors attributable to star-to-star differences in CN band strengths. Similarly, C(4245) colors also vary in a manner anticorrelated with C(4142), as would be expected from a CN/CH band strength anticorrelation.
The photometry is analyzed using model-based synthetic DDO colors with the following results: 1) The CN-weak stars as a group are best fit by models with [C/Fe] = -0.1 and [N/Fe] = 0.0, while the CN-strong stars are consistent with [C/Fe] = -0.3 and [N/Fe] = +1.4. 2) No appreciable change in surface C or N abundances takes place over the 4 magnitudes observed. This implies that the bulk of the C and N abundance differences observed among the evolved giants are not the result of mixing during the later stages of red giant branch ascent. In these aspects, M71 also appears remarkably similar to 47 Tucanae, a cluster of similar metallicity yet significantly greater mass.
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