Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasj...46..395t&link_type=abstract
PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 46, no. 4, p. 395-413
Astronomy and Astrophysics
Astronomy
55
A Stars, Abundance, F Stars, Line Spectra, Sodium, Stellar Atmospheres, Stellar Envelopes, Supergiant Stars, Astronomical Spectroscopy, Hydrogen, Infrared Astronomy, Local Thermodynamic Equilibrium, Stellar Evolution, Stellar Mass, Visible Spectrum
Scientific paper
A comprehensive non-local thermodynamic equilibrium (non-LTE) analysis of Na I lines was performed in order to investigate the photospheric abundance of sodium in typical bright A-F supergiants. Along with the strongest subordinate line, Na I lambda 8195, newly observed for this study, which enabled us to determine the Na abundance of A supergiants for the first time, we also reanalyzed the available data of other weaker lines published so far. It was revealed that F supergiants (Teff is greater than or approximately equal to 6000 K and less than or approximately equal to 7500 K) generally show a moderate Na-excess of (Na/H) greater than or approximately equal to 0.0 and less than or approximately equal to 0.5 and that the extent of this anomaly tends to increase with the stellar mass, confirming the well-known spectroscopic evidence already suggested from past analyses of F, G, K supergiants. Also, such a derived amount of overabundance was found to be consistent with a prediction based on the standard theory for the dredge-up and the mixing of the NeNa-cycle products from the H-burning region without requiring any ad-hoc hypotheses. Regarding the A-type sypergiants, a general tendency was found that Na is largely overabundant by 0.7-0.8 dex in most cases; though, unlike the F stars, no apparent mass-dependence appears to exist. This evidence may suggest that the envelope of these A supergiants also experienced some kind of mixing during the course of their past evolution, the mechanism for which is yet to be further investigated.
Takada-Hidai Masahide
Takeda Yoichi
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