The nature of the newly discovered DO white dwarf RE 0503 – 289

We report the discovery of a hot DO white dwarf, RE 0503−289, which lies in a region of very low interstellar H I density. The star was found independently by the ROSAT EUV and Edinburgh-Cape surveys. It lies within 1° of the hot DA white dwarf RE 0457−281 which we have reported as having the lowest directly measured H I column. A follow-up observation made using the Voyager 2 ultraviolet spectrometer reveals a strong continuum shortward of the 912-A Lyman limit, and hence a similarly low hydrogen column density of 1.3×10 17 atom cm −2 . Optical and UV spectroscopy gives a temperature in the range 60000-80000 K and a carbon abundance ≃1 per cent