EDP Sciences
Free Access
Volume 394, Number 2, November I 2002
Page(s) 647 - 651
Section Stellar atmospheres
DOI https://doi.org/10.1051/0004-6361:20021141

A&A 394, 647-651 (2002)
DOI: 10.1051/0004-6361:20021141

Quasi-molecular lines in Lyman wings of cool DA white dwarfs

Application to ${\it FUSE}$ observations of G $\,$231-40
G. Hébrard1, N. F. Allard1, 2, I. Hubeny3, S. Lacour4, 1, R. Ferlet1 and A. Vidal-Madjar1

1  Institut d'Astrophysique de Paris, CNRS, 98 ${\rm bis}$ boulevard Arago, 75014 Paris, France
2  Observatoire de Paris-Meudon, LERMA, 92195 Meudon Principal Cedex, France
3  NOAO, 950 North Cherry Avenue, Tucson, AZ 85726, USA
4  Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

(Received 3 April 2002 / Accepted 5 August 2002 )

We present new theoretical calculations of the total line profiles of Lyman  $\alpha$ and Lyman  $\beta$ which include perturbations by both neutral hydrogen and protons and all possible quasi-molecular states of H 2 and H 2+. They are used to improve theoretical modeling of synthetic spectra for cool DA white dwarfs. We compare them with FUSEobservation of G $\,$231-40. The appearance of the line wings between Lyman  $\alpha$ and Lyman  $\beta$ is shown to be sensitive to the relative abundance of hydrogen ions and neutral atoms, and thereby to provide a temperature diagnostic for stellar atmospheres and laboratory plasmas.

Key words: line: profiles -- radiation mechanisms: general -- stars: atmospheres -- stars: individual: G231-40 -- white dwarfs -- ultraviolet: stars

Offprint request: G. Hébrard, hebrard@iap.fr

© ESO 2002