Oxygen isotopic abundances in evolved stars. IV - Five K giants

Details Oxygen isotopic abundances in evolved stars. IV - Five K giants Oxygen isotopic abundances in evolved stars. IV - Five K giants

Feb 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apj...325..768h&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 325, Feb. 15, 1988, p. 768-775. Research supported by the Robert A. Welch F

Astronomy and Astrophysics

Astrophysics

56

Abundance, Asymptotic Giant Branch Stars, K Stars, Late Stars, Oxygen Isotopes, Helium, Stellar Envelopes, Stellar Interiors

Scientific paper

Oxygen isotopic ratios have been measured in the atmospheres of Alpha UMa, Beta Gem, Beta UMi, Alpha Ari, and Alpha Ser. It is shown that some of the stars in this and previous samples have probably experienced the helium core flash, and that the O-16/O-17 ratios tend to confirm that 'extramixing' of CNO-cycled material into the stars' envelopes has occurred as a result of the flash. The oxygen isotopic ratios are much smaller than the anomalously high ratios seen in stars in the later thermal-pulsing state of evolution. Hence, the anomalous ratios cannot be explained by the helium core flash. It is proposed that they are due to the addition by the third dredge-up mechanism of helium-burned material which is devoid of both O-17 and O-18 and therefore dilutes the O-17 and O-18 abundances acquired during earlier evolutionary stages. This process may also explain the oxygen isotope ratios seen in barium stars, if these are formed by mass transfer from a thermally pulsing binary companion.

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