期刊
ASTRONOMY & ASTROPHYSICS
卷 443, 期 3, 页码 L25-L28出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361:200500195
关键词
line : formation; stars : atmospheres; stars : fundamental parameters; stars : individual : V652 Her, HD144941
Quantitative analyses of low-mass hydrogen-deficient (super-)giant stars - so-called extreme helium stars - to date face two major difficulties. First, theory fails to reproduce the observed helium lines in their entirety, wings and line cores. Second, a general mismatch exists for effective temperatures derived from ionization equilibria and from spectral energy distributions. Here, we demonstrate how the issue can be resolved using state-of-the-art non-LTE line-formation for these chemically peculiar objects. Two unique high-gravity B-type objects are discussed in detail, the pulsating variable V652 Her and the metal-poor star HD144941. In the first case atmospheric parameters from published LTE analyses are largely recovered, in the other a systematic off. set is found. Hydrogen abundances are systematically smaller than previously reported, by up to a factor similar to 2. Extreme helium stars turn out to be important testbeds for non-LTE model atoms for helium. Improved non-LTE computations show that analyses assuming LTE or based on older non-LTE model atoms can predict equivalent widths, for the He. 10 830 angstrom transition in particular, in error by up to a factor similar to 3.
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