Constraints from stellar models on mixing as a viable explanation of abundance anomalies in globular clusters

The authors have attempted to explore the hypothesis that differences in the depth of stellar interior mixing can account for the star-to-star differences in C and N abundances that are commonly observed within globular clusters. The canonical first dredge-up episode predicted by standard stellar models does not reproduce the nitrogen enhancements seen among the CN-enriched giants in most globular clusters. As a result, stellar models in which the envelopes have been artificially mixed to some arbitrary depth have been used in an attempt to identify possible epochs during the evolution of a cluster star during which deep mixing might be able to produce the observed abundance patterns.