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Issue A&A
Volume 405, Number 3, July III 2003
Page(s) 1153 - 1156
Section Celestial mechanics and astrometry
DOI http://dx.doi.org/10.1051/0004-6361:20030715



A&A 405, 1153-1156 (2003)
DOI: 10.1051/0004-6361:20030715

Modeling of the Lyman $\gamma$ satellites in FUSE spectra of DA white dwarfs

G. Hébrard1, N. F. Allard1, 2, J. F. Kielkopf3, P. Chayer4, J. Dupuis4, J. W. Kruk4 and I. Hubeny5

1  Institut d'Astrophysique de Paris, CNRS, 98bis 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
4  Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
5  NOAO, 950 North Cherry Avenue, Tucson, AZ 85726, USA

(Received 1 April 2003 / Accepted 7 May 2003)

Abstract
We present new theoretical calculations of the line profile of Lyman  $\gamma$ that include transitions in which a photon is absorbed by a neutral hydrogen atom while it interacts with a proton. Models show that two absorption features located near 992 Å and 996 Å are due to H-H + collisions. These quasi-molecular satellites are similar to those that were identified in the wings of Lyman  $\alpha$ and Lyman  $\beta$ lines of hydrogen-rich white dwarfs. We compute synthetic spectra that take account of these new theoretical profiles and compare them to the spectra of four DA white dwarfs that were observed with FUSE. The models predict the absorption features that are observed in the wing of Lyman  $\gamma$ near 995 Å, and confirm that these features are quasi-molecular satellites.


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

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

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