1995A&A...300L...5N

We present an analysis of a hig-resolution FUV spectrum (912...1170Angstroems) of the cool DO white dwarf HD 149499 B. Observations were performed with the Berkeley EUV/FUV spectrometer of the ORFEUS experiment. The analysis, performed with a grid of LTE model atmospheres, yielded the basic parameters Teff = 49500±500K and log g = 7.97±0.08. The photospheric hydrogen Lyman lines in the FUV spectrum indicate the presence of hydrogen: log nH/nHe =-0.65±0.12.The implications of this finding for the spectral evolution of white dwarfs are discussed. A check of the LTE assumption was performed by a comparison with NLTE atmospheres calculated for appropriate parameters. The interstellar components of the hydrogen Lyman lines are used for an estimate of the hydrogen column towards the HD 149499 system: N_H about 1x10¹⁹/cm2.