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Non-LTE analysis of extremely helium-rich stars. The hot sdO stars LSE 153, 259 and 263Results of a non-LTE fine analysis based mainly on high-resolution CASPEC spectra for three extremely helium-rich sdO stars are discussed in order to explain hydrogen deficiency in single stars. High temperature (Teff = 70,000 to 75,000 K) and a position in the log Teff - log g diagram were found close to the Eddington limit. Various abundance estimates are derived for hydrogen (upper limits only), carbon, nitrogen, and magnesium. Hydrogen is reduced to less than 10 percent by number in LSE 153 and LSE 263, and to less than 5 percent in LSE 259. The hydrogen deficiency is accompanied by nitrogen- and carbon-enrichment in LSE 153 and LSE 259 only. In LSE 263, carbon is depleted by about 1 dex. Stellar masses obtained by assuming that a core mass-luminosity relation holds for these stars, were found to be in the range 0.6-0.9 solar mass, yielding luminosities log L/L:solar = 3.7-4.5. Two of the program stars (LSE 153 and 259) appear to be possible successors of the R CrB and helium B stars, whereas the third star (LSE 263) displays a much lower carbon content in its photosphere making it an exceptional case among the known hydrogen deficient stars.
Document ID
19900025919
Document Type
Reprint (Version printed in journal)
Authors
Husfeld, D. (Ludwig-Maximilians-Univ. Munich, Germany)
Butler, K. (Muenchen, Universitaet Munich, Federal Republic of Germany, United States)
Heber, U. (Kiel, Universitaet Federal Republic of Germany, United States)
Drilling, J. S. (Louisiana State University Baton Rouge, United States)
Date Acquired
August 14, 2013
Publication Date
September 1, 1989
Publication Information
Publication: Astronomy and Astrophysics
Volume: 222
Issue: 2-Jan
ISSN: 0004-6361
Subject Category
ASTROPHYSICS
Funding Number(s)
CONTRACT_GRANT: DFG-KU-474/13-1
CONTRACT_GRANT: NSF AST-85-14574
CONTRACT_GRANT: DFG-HU-39/21-1
CONTRACT_GRANT: NAG5-71
CONTRACT_GRANT: DFG-KU-474/9-2
Distribution Limits
Public
Copyright
Other