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Session 3 - Clusters.
Display session, Monday, June 10
The Galactic globular cluster 47 Tucanae has long been known to be inhomogeneous in the relative CN band strengths of otherwise similar stars. Explanations of this observation (as well as the CN band strength differences observed in other clusters) are typically divided into a) an episode of deep dredge-up into a region above the H-burning shell which is actively undergoing CN-cycle nucleosynthesis, or b) the effects of a primordial process which modified the distribution of C and N early in the cluster history. In order to examine the possible roles of both scenarios, CCD BV and DDO photometry has been obtained with the CTIO 0.9-m telescope for an 11 x 11 arcminute field centered 13 arcminutes NE of the cluster center. From this sample, accurate DDO C(4142) colors have been used to characterize the CN band strengths of roughly 300 cluster giants down to M_v = +2.5. Analysis of this data will take two approaches. First, the C(4142) colors will be compared against model colors to explore the possibility of differing C and N abundances as a function of evolutionary state, as would be expected from a deep mixing process. Second, the relative distribution of CN-strong and CN-weak stars will be determined as a function of radial distance from the cluster center. The presence of a such spatial dependence will suggest the possibility of a primordial source, or at least the operation of some process unique to the cluster environment.
Program listing for Monday