A new hot DA white dwarf in a region of exeptionally low H I density

We report the discovery of the hot DA white dwarf RE 0457−281 which has the lowest line-of-sight neutral hydrogen column density yet measured. The star was found independently by the ROSAT EUV, Montreal-Cambridge-Tololo and Edinburgh-Cape surveys. With an effective temperature of 60 700 K and very soft EUV spectrum, this white dwarf resembles the well-studied hot DA white dwarf G 191−B2B. A follow-up observation made using the Voyager 2 UV spectrometer reveals a strong continuum shortward of the 912-A Lyman limit from which we deduce that the neutral hydrogen column density is 1.3×10 17 atom cm −2