Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...235..234d&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 235, no. 1-2, Aug. 1990, p. 234-241.
Astronomy and Astrophysics
Astrophysics
50
Hot Stars, Milky Way Galaxy, O Stars, Star Distribution, Stellar Atmospheres, Subdwarf Stars, Helium, Nonequilibrium Thermodynamics, Stellar Evolution, Stellar Luminosity, Stellar Spectra, Stellar Temperature
Scientific paper
The visual spectra of 15 extremely helium rich subdwarf O-stars are analyzed. Effective temperatures and gravities are determined by means of a new grid of helium and hydrogen line-blanketed non-LTE model atmospheres calculated with the accelerated lambda iteration. Effective temperatures cluster around 45,000 K and 65,000 K. Gravities range from log g = 4.8 to log g = 6.0. Hydrogen is detected in 5 stars. Upper limits to the hydrogen content are derived for the others. From these spectroscopic results first conclusions about the evolutionary status of these stars can be drawn. The program stars probably evolve from the extended or blue horizontal branch. Mixing induced by thermal pulses might account for the helium enrichment.
de Boer Klaas. S.
Dreizler Stefan
Heber Uli
Moehler Sabine
Werner Kirstin
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