Nitrogen variations on the main sequence of 47 tucanae: implications from stellar structure theory
We present evolutionary calculations of a 0.9 M/sub sun/ metal-poor star in which the outer layers are artifically mixed throughout the main-sequence lifetime. For the case where the mixed region contains 85% of the mass of the star, evolution toward the subgiant branch is relatively unaffected but no significant enhancement of the surface nitrogen abundance occurs. Alternatively, for the case of deeper mixing, significant surface nitrogen enhancements are produced but the star evolves as a blue straggler and does not become a red giant in a normal way. Thus the observations of large nitrogen abundance variations among main-sequence stars and subgiants in the globular cluster 47 Tuc are unlikely to be the result of deep envelope mixing on the main sequence. Mixing at an advanced phase of evolution and mass transfer in close binaries also seem unlikely. We conclude therefore that the most plausible explanation of the observed variations is that they are primordial in origin, that is, they reflect the presence of nitrogen abundance inhomogeneities in the protocluster gas cloud. Subject headings: clusters: globular: nucleosynthesis: stars: abundances: stars: interiors: stars: weak-line
- Research Organization:
- Yale University Observatory
- OSTI ID:
- 6866047
- Journal Information:
- Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 259:1; ISSN ASJOA
- Country of Publication:
- United States
- Language:
- English
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