Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aj....104.1986v&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 104, no. 5, p. 1986-1996.
Astronomy and Astrophysics
Astronomy
48
Carbon Isotopes, Giant Stars, Heavy Elements, Nitrogen, Oxygen, Abundance, Cool Stars, Stellar Envelopes
Scientific paper
Complete CNO abundances are obtained for a sample of red-giant CH stars. Analysis of the abundances shows that there are large excesses of carbon and nitrogen in the atmosphere while all indications are that the oxygen abundances follow the normal pattern observed among field G and K giants. A correlation between the C/N and C-13/C-12 seems to exist in the red giant CH stars. Taken together, the excess of C and N nuclei, the large C/O ratios, and the C-12/C-13 and C/N ratios favor a scenario for the creation of CH stars in which Roche lobe overflow followed by some mechanism which mixes the accreted material into regions of the star, where it participates in CN burning to some degree. The s-process element abundance patterns of the CH stars are investigated, and it is found that the overall level of enhancement is greater in the CH stars than in barium stars. The distribution of the element favors the heavy s-process peak more than in barium stars. The abundance pattern are best modeled by exposure of s-process seed nuclei to a single irradiation. These abundance patterns are shown to arise naturally from the operation of the C-13 neutron source in low-mass low-metallicity AGB stars.
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