DISCOVERY OF A WHITE-DWARF COMPANION (MS0354.6-3650 EQUAL EUVE J0356-366) TO A G2V STAR

We present x-ray, ultraviolet, and optical observations of the mysteri ous EUV/soft x-ray source EUVE 50356-336 (= MS0354.6-3650). Initial Ei nstein observations identified this source with a cluster of galaxies, but the relatively high source count rate in the Extreme Ultraviolet Explorer (EUVE) 100 Angstrom band and the lack of variability hinted t hat EUVE J0356-3650 might be a white dwarf; the UK Schmidt plate of th e field surrounding this object found a 12.45 magnitude G2V star that could hide a compact companion. This hypothesis was confirmed in an IU E ultraviolet spectrum that shows the definite signature of a hydrogen -rich white dwarf (DA). A model atmosphere analysis shows that the DA star is hot (T-eff greater than or equal to 52,000 K) and may have a l ow abundance of heavy elements. We show that the G2V star and the DA s tar form a physical pair at a distance of 400 pc and therefore add to the list of white dwarf plus luminous main sequence star binaries disc overed in EUV surveys. (C) 1996 American Astronomical Society.