Oxygen Abundances in Late-B through F Supergiants

Details Oxygen Abundances in Late-B through F Supergiants Oxygen Abundances in Late-B through F Supergiants

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998pasj...50..629t&link_type=abstract

Publications of the Astronomical Society of Japan, v.50, p.629-638.

Astronomy and Astrophysics

Astronomy

28

Non-Lte Effect, Stars: Abundances (Oxygen), Stars: Atmospheres, Stars: Evolution:, Stars: Supergiants

Scientific paper

A spectral-synthesis analysis was performed for twenty-six late-B through F supergiants (including Cepheids) in order to determine their photospheric oxygen abundances from the O I 6156--8 feature, while taking into account the non-LTE effect, which is progressively T_eff-dependent from < 0.1 dex for F-type supergiants to ~ 0.4 dex for late-B ones in terms of the non-LTE abundance correction. The resulting oxygen abundances show a moderate underabundance relative to the Sun ([O/H] ~ -0.3) along with a remarkably small scatter (within +/- 0.1 dex) over this wide temperature range. Considering the recent evidence that the solar oxygen abundance is mildly enhanced by 0.2--0.3 dex relative to that of the galactic gas which forms young stars, we conclude that the original O-composition in the atmosphere of these supergiants had suffered almost no appreciable alteration during their past evolutionary history, even though signs of significant mixing of CN-cycle or NeNa-cycle products are evident. This excludes the possibility of any global-mixing mechanism, such that producing a significant reduction of oxygen due to a deep dredge-up of considerable ON-processed material, whatever the details of the envelope-mixing process for these relatively massive stars may be.

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