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Publications of the Astronomical Society of Australia Publications of the Astronomical Society of Australia Society
Publications of the Astronomical Society of Australia
RESEARCH ARTICLE

Understanding AGB Carbon Star Nucleosynthesis from Observations


Publications of the Astronomical Society of Australia 20(4) 314 - 323
Published: 19 December 2003

Abstract

Recent advances in the knowledge of the evolutionary status of asymptotic giant branch (AGB) stars and of the nucleosynthesis processes occurring in them are discussed, and used to interpret abundance determinations for s-process elements, lithium and CNO isotopes in several types of AGB stars. We focus our attention mainly on carbon-rich AGB stars. By combining these different constraints we conclude that most carbon stars in the solar neighborhood are of low mass (M≤3 M), their abundances being a consequence of the operation of thermal pulses and the third dredge-up. However, the observed abundances in carbon stars of the R and J types cannot be explained by this standard scenario. These stars may not be on the AGB, but possibly in the core-He burning phases; their envelopes may have been polluted with nuclear ashes of the core-He flash, followed by CNO re-processing enhancing 13C. Observational evidence suggesting the operation of non-standard mixing mechanisms during the AGB phase is also discussed.

Keywords: nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: AGB — stars: carbon — stars: evolution

https://doi.org/10.1071/AS03021

© ASA 2003

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