Oxygen 6156-8 Angstroms Triplet in Chemically Peculiar Stars of the Upper Main Sequence: Do HgMn Stars Show an Oxygen Anomaly?

Details Oxygen 6156-8 Angstroms Triplet in Chemically Peculiar Stars of the Upper Main Sequence: Do HgMn Stars Show an Oxygen Anomaly? Oxygen 6156-8 Angstroms Triplet in Chemically Peculiar Stars of the Upper Main Sequence: Do HgMn Stars Show an Oxygen Anomaly?

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999pasj...51..961t&link_type=abstract

Publications of the Astronomical Society of Japan, v.51, p.961-976.

Astronomy and Astrophysics

Astronomy

9

Spectroscopy, Stars: Abundances, Stars: Atmospheres, Stars: Chemically Peculiar, Stars: Early-Type

Scientific paper

An extensive spectrum-fitting analysis in the lambda ~ 6150 Angstroms region was performed for forty late-B and A chemically peculiar (HgMn, Ap, Am, weak-lined) and normal stars of the upper main sequence, in order to quantitatively establish the abundance of oxygen from the O I 6156-8 triplet and to study its behavior/anomaly for each peculiarity group, where special attention was paid to HgMn-type stars. Magnetic Ap variables (Si or SrCrEu type) generally show a remarkably large oxygen depletion (by ~ -1.6 dex to ~ -0.4 dex relative to the solar abundance), and classical Am stars also show a clear underabundance (by ~ -0.6 dex on the average). In contrast, the oxygen abundance in HgMn stars, exhibiting only a mild deficiency relative to the Sun typically by ~ 0.3-0.4 dex, is not markedly different from the tendency of normal stars, also showing a subsolar abundance ([O/H] =~ -0.2). In view of the recent observational implication that the present solar oxygen abundance is enriched by ~ 0.2-0.3 dex relative to the interstellar gas (from which young stars are formed), and thus unsuitable for the comparison standard, we concluded that the extent of the average O-deficiency in HgMn stars is appreciably reduced down to only ~ 0.1-0.2 dex (i.e., not much different from the initial composition), which contrasts with their well-known drastically large N-depletion. Yet, as can be seen from the delicate and tight O vs. Fe anticorrelation, this marginal deficiency should be real, and thus some physical process simultaneously producing O-depletion/Fe-enrichment must have actually worked in the atmosphere of HgMn stars.

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