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Non-LTE line-blanketed model atmospheres of hot stars. 2: Hot, metal-rich white dwarfs
Lanz, T.; Hubeny, I.
AA(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AB(NASA. Goddard Space Flight Center, Greenbelt, MD, US)
The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 439, no. 2, p. 905-916 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Abundance, Atmospheric Models, Local Thermodynamic Equilibrium, Metallic Stars, Stellar Atmospheres, Stellar Models, White Dwarf Stars, Carbon, Equilibrium Equations, Hydrogen, Hydrostatics, Iron, Line Spectra, Metallicity, Radiative Transfer
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We present several model atmospheres for a typical hot metal-rich DA white dwarf, Teff = 60,000 K, log g = 7.5. We consider pure hydrogen models, as well as models with various abundances of two typical 'trace' elements-carbon and iron. We calculte a number of Local Thermodynamic Equilibrium (LTE) and non-LTE models, taking into account the effect of numerous lines of these elements on the atmospheric structure. We demostrate that while the non-LTE effects are not very significant for pure hydrogen models, except for describing correctly the central emission in H-alpha they are essential for predicting correctly the ionization balance of metals, such as carbon and iron. Previously reported discrepancies in LTE abundances determinations using C III and C IV lines are easily explained by non-LTE effects. We show that if the iron abundance is larger than 10-5, the iron line opacity has to be considered not only for the spectrum synthesis, but also in the model construction itself. For such metal abundances, non-LTE metal line-blanketed models are needed for detailed abundance studies of hot, metal-rich white dwarfs. We also discuss the predicted Extreme Ultraviolet (EUV) spectrum and show that it is very sensitive to metal abundances, as well as to non-LTE effects.

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