Identification of the 1400 and 1600 A features observed in the ultraviolet spectra of DA white dwarfs

Abstract

The λ1600 absorption feature in the spectra of cool DA white dwarf stars has been identified as a resonance broadening of Lyα due to the hydrogen quasi molecule. Likewise, the λ1400 absorption feature in the spectra of cool and moderately warm DA white dwarf stars appears to be due to a Lyα satellite line arising from the hydrogen ion quasi molecule. The strength of both features is gravity sensitive and therefore promises to be an excellent indicator of surface gravity.