QUASI-MOLECULAR SATELLITES OF Lyβ IN THE SPECTRUM OF THE DA WHITE DWARF WOLF 1346

摘要

We present new FUV/UV observations of the DA white dwarf Wolf 1346 obtained with the Hopkins Ultraviolet Telescope. The atmospheric parameters of this object are estimated from a fit of model atmospheres to several optical spectra to be T_(eff) = 20,000 K, log g = 7.90. From the optical spectrum this star is a normal DA without any indications for chemical elements other than hydrogen. The hydrogen line Lyβ, however, shows a very unusual shape, with a steep red wing and two absorption features on this wing. The shape is reminiscent of the effects of quasi-molecular line broadening, as observed in Lyα in cooler DA white dwarfs. We show that this is indeed the correct explanation, by identifying four quasi-molecular satellites caused through perturbations by the H~+ ion (H_2~+ quasi-molecule). The steep red wing is caused by the exponential decline of the line profile beyond the satellite most distant from the line center at 1078 A.