On the Carbon and Nitrogen Abundances of 47 Tucanae's Main-Sequence Stars

We report the results of an analysis of CN and CH band strengths among alarge sample of 47 Tucanae main-sequence and turn-off stars presented earlierby Harbeck et al. The resulting C and N abundances derived from syntheticspectra demonstrate: 1) A strongly anti-correlated relationship between [C/Fe] and [N/Fe] with theCN-strong stars exhibiting depleted carbon and enhanced nitrogen. 2) The abundances of both elements agree remarkably well with those foundamong the evolved red giants of the cluster implying little change in surfaceabundances from at least Mv ~ +6.5 to the tip of the red giant branch. 3) The pattern of C-depletions and N-enhancements are quite similar to thoseseen among the turn-off stars of M71, a cluster of almost identical metallicitybut lower central concentration and escape velocity. At the same time, similarif not smaller N-enhancements and larger C-depletions are evident among likestars in the more metal-poor cluster M5. We interpret these results, as did Harbeck et al., as evidence of theoperation of some pollution/accretion event early in the cluster history - themost likely source being AGB ejecta. However, the present results rule outsimple surface pollution and suggest that a substantial fraction of the presentstars' masses must be involved.Comment: To be published in The Astronomical Journal (replaced to correct error in author list