Laboratory Detection of the Lyβ 1150 Å Quasi-molecular Satellite Seen in Far Ultraviolet Spectroscopic Explorer Observations of the White Dwarf G226-29

We report a laboratory measurement of the 1150 Å collision-induced quasi-molecular satellite of Lyβ. It was first identified in Far Ultraviolet Spectroscopic Explorer observations of the cool DA white dwarf G226-29. The satellite, predicted by theoretical calculations of the complete profile of the hydrogen Lyα and Lyβ lines, arises from transitions occurring during close collisions of hydrogen atoms. Fits of model atmospheres with these profiles to observed spectra provide accurate constraints on stellar temperature and gravity. The comparison here of the far-ultraviolet absorption spectrum of a laser-produced hydrogen plasma with the theoretical absorption profiles and a model of the plasma confirms the underpinning atomic and molecular theory.