Spectral Monitoring of HS 0209+0832 a DAB White Dwarf in the DB Gap
We report results of a spectral monitoring campagne of the DAB white dwarf HS 0209+0832, for which helium line profile variations were reported earlier (Heber et al. 1997). This finding is confirmed by our discovery of a second epoch (October 1997) of unusually low helium line strength and of their subsequent recovery. The observed changes in line strength correspond to a variation of the (average) helium abundance by a factor of 2.