Free Access
Volume 424, Number 1, September II 2004
Page(s) 347 - 354
Section Atomic, molecular and nuclear data
Published online 17 August 2004

A&A 424, 347-354 (2004)
DOI: 10.1051/0004-6361:20040427

Temperature dependence of the Lyman  $\alpha$ line wings in cool hydrogen-rich white dwarf atmospheres. Application to ZZ Ceti white dwarf spectra

N. F. Allard1, 2, J. F. Kielkopf3 and B. Loeillet1

1  Institut d'Astrophysique de Paris, CNRS, 98 bis boulevard Arago, 75014 Paris, France
2  Observatoire de Paris-Meudon, LERMA, 92195 Meudon Principal Cedex, France
3  Department of Physics, University of Louisville, Louisville, KY 40292, USA

(Received 11 March 2004 / Accepted 29 April 2004)

Theoretical Lyman  $\alpha$ absorption profiles show a significant dependence on temperature of the H 2 satellite at 1600 Å, whereas the H 2+ satellite at 1400 Åremains unchanged. The use of opacities calculated with different approximations concerning the electric dipole transition moment (constant, dependent on interatomic distance, and modulated by the Boltzmann factor) lead to very different synthetic absorption spectra. Our new Lyman  $\alpha$ profiles over the ZZ Ceti range of temperatures have been used to synthesize theoretical spectra which compare very well to existing HST spectra.

Key words: line: profiles -- stars: atmospheres -- stars: white dwarfs -- ultraviolet: stars

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© ESO 2004

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