Query : 2005A&A...443L..25P

2005A&A...443L..25P - Astronomy and Astrophysics, volume 443, L25-28 (2005/12-1)

Extreme helium stars: non-LTE matters. Helium and hydrogen spectra of the unique objects V652 Her and HD 144941.


Abstract (from CDS):

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 HD 144941. In the first case atmospheric parameters from published LTE analyses are largely recovered, in the other a systematic offset is found. Hydrogen abundances are systematically smaller than previously reported, by up to a factor ∼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 HeI10830Å transition in particular, in error by up to a factor ∼3.

Abstract Copyright:

Journal keyword(s): line: formation - stars: atmospheres - stars: fundamental parameters - stars: individual: V652 Her, HD 144941

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 HD 144941 pA* 16 09 24.5513020968 -27 13 38.184011148 9.45 10.17 10.02     B8 88 1
2 V* V652 Her pA* 16 48 04.6934854032 +13 15 42.420402252   10.31 10.51     ~ 138 0

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