Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984a%26a...130..119h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 130, no. 1, Jan. 1984, p. 119-130.
Astronomy and Astrophysics
Astrophysics
151
B Stars, Stellar Atmospheres, Stellar Gravitation, Stellar Spectra, Stellar Temperature, Subdwarf Stars, Astrometry, Helium, Iue, Main Sequence Stars, Radial Velocity, Stellar Evolution, Ultraviolet Spectra
Scientific paper
The spectra of eight high galactic latitude B stars, suspected to be subluminous, are analyzed for effective temperature, gravity, and helium to hydrogen ratio. Model atmospheres include (LTE) UV line blanketing (for T/eff/ less than or equal to 30,000 K) and NLTE effects (for T/eff/ greater than 30,000 K). Among the eight confirmed subdwarfs, six have temperatures around 26,000 K. Two objects are considerably hotter (34,000 K and 41,000 K) and belong to the sdOB subclass. Gravity ranges from log g = 5.0 to 5.5 for the sdB's, the sdOB's having log g = 5.7 and 6.0, respectively. Helium is strongly depleted in the sdB's and sdOB's: from He I 4471 (if present) the number fraction obtained is 0.0016 n(He)/n(H) = 0.0016-0.016. From the g, T(eff)-diagram it is concluded that the subluminous B stars and sdOB stars are (generalized) helium main sequence stars with approximately 0.5 solar mass. The helium deficiency of the envelope is brought about by diffusion.
Heber Uli
Hunger Kurt
Jonas G.
Kudritzki Rolf Peter
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