Far ultraviolet spectroscopic explorer observations of G226-29: First detection of the H₂ quasi-molecular satellite at 1150 Å

We present new far-ultraviolet observations of the pulsating DA white dwarf G226-29 obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This ZZ Ceti star is the brightest one of its class and the coolest white dwarf observed by FUSE. We report the first detection of the broad quasi-molecular collision-induced satellite of Lyβ at 1150 Å, an absorption feature that is due to transitions that take place during close collisions of hydrogen atoms. The physical interpretation of this feature is based on recent progress of the line-broadening theory of the far wing of Lyβ. This predicted feature had never been observed before, even in laboratory spectra.