New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions

¹ Observatoire de Paris, GEPI, UMR 8111, CNRS, 61, Avenue de l'Observatoire, 75014 Paris, France e-mail: nicole.allard@obspm.fr
² Department of Physics, Tbilisi State University, Chavchavadze Avenue 3, 0128 Tbilisi, Georgia
³ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

Received: 16 May 2009
Accepted: 6 July 2009

Abstract

Context. Quasi-molecular line satellites in the red wings of Lyman series of atomic hydrogen have been identified in the spectra of hydrogen-rich white dwarfs. These features are produced by radiative collisions.

Aims. Structures observed about 995 Åin the Lyman-γ wing of hot white dwarfs have been shown to be caused by quasi-molecular absorption of H molecules.

Methods. Improvements to previous theoretical calculations of the Lyman-γ line profiles can be achieved by using a unified theory that takes into account the dependence of the dipole moments on internuclear distance during the collision.

Results. For the first time, we have computed the transition dipole moments. We measure a significant increase in the region of the formation of the satellites, which alters the general shape of the profile.

Conclusions. A large increase in the strength of the two main satellites at 992 and 996 Å leads to a deeper broad absorption in the synthetic spectra, which should improve the comparison with observation as previous predicted Lyman-γ satellites were too weak.