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

Application to observations of G 231–40

¹ Institut d'Astrophysique de Paris, CNRS, 98 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

Corresponding author: G. Hébrard, hebrard@iap.fr

Received: 3 April 2002
Accepted: 5 August 2002

Abstract

We present new theoretical calculations of the total line profiles of Lyman α and Lyman β which include perturbations by both neutral hydrogen and protons and all possible quasi-molecular states of H₂ and H. 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 α and Lyman β 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.