Other
Scientific paper
Mar 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...338..417m&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 338, March 1, 1989, p. 417-423. Research supported by NSERC.
Other
31
Helium, Hot Stars, Nonequilibrium Thermodynamics, Radiative Transfer, Stellar Atmospheres, Subdwarf Stars, Atmospheric Models, B Stars, Gravitational Effects, Heuristic Methods, O Stars
Scientific paper
Detailed non-LTE radiative accelerations on He are calculated in non-LTE model atmospheres with parameters appropriate for sdOB stars. Detailed statistical equilibrium calculations are carried out in order to obtain He occupation numbers. For N(He)/N(H) = 0.1, the radiative accelerations are calculated to be always at least 10 times smaller than gravity in the line-forming region, so that He should always be underabundant, as observed in these objects. However, the radiative acceleration remains smaller than gravity even at the observed underabundances of He so that, in the absence of competing processes, diffusion should lead to larger underabundances than observed. The observed He abundances in sdOB stars cannot be supported by radiative acceleration alone. Other processes, such as mass loss, must be involved.
Bergeron Pierre
Heber Uli
Michaud Georges
Wesemael François
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