Carbon isotope ratios in field Population II giant stars

Details Carbon isotope ratios in field Population II giant stars Carbon isotope ratios in field Population II giant stars

Dec 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...311..826s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 311, Dec. 15, 1986, p. 826-842.

Statistics

Computation

119

Carbon Isotopes, Dwarf Stars, Giant Stars, Late Stars, Stellar Spectrophotometry, Abundance, Stellar Evolution, Stellar Interiors

Scientific paper

Carbon isotope ratios have been derived from high-resolution spectra of the CH G-band in 15 very metal-poor Population II giant stars and two similar dwarf stars. Many of the giants possess very low C-12/C-13 ratios, some approaching the CN cycle equilibrium value. The metal-poor dwarfs do not have detectable CH-13 features; thus the low carbon isotope ratios in the giants probably are due to their internal evolutions. These results strongly support the idea that at least part of the anomalously low C/N values in Population II giants arises from very efficient mixing of their envelopes into the CN cycle burning layers. Detailed calculations of the expected CNO surface abundances in Population II giants in different evolutionary states have been performed. These computations demonstrate that the observed carbon isotope ratios cannot be produced during the first dredge-up mixing phases in low-mass, low metal abundance stars. Numerical experiments show that theoretical and observational results can be brought into agreement with artificially induced extra mixing. An agent to provoke this additional mixing has not been identified with certainty yet, although internal stellar rotation is a promising candidate.

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