A New K0 IV--V Plus White Dwarf Binary in The EUVE Survey

We present far ultraviolet and optical spectroscopy of the Extreme Ultraviolet Explorer (EUVE) survey source EUVE J0702+129 showing a composite K0 star plus DA white dwarf spectrum. International Ultraviolet Explorer spectra show continuum emission from a hot white dwarf (T_eff =30-40,000 K) and a rising contribution from the K0 star at lambda >= 2500 Angstroms. High resolution optical spectroscopy reveals a moderate level of activity with Ca II H & K emission; application of the Wilson-Bappu relation indicates that the secondary star is slightly above the main-sequence (K0 IV--V). Both objects are found at a distance of ~ 100 pc and probably constitute a physical pair. The EUV emission is probably dominated by the white dwarf, but the late-type star possibly contributes at higher energy. Interesting parallels are drawn with other DA+K0 pairs with moderately active secondaries such as HD 18131 and HR 1608. The present discovery as well as other recent ones demonstrate the existence of a large population of white dwarfs hidden by evolved companions (III--IV). This work is supported by NASA grant NAG-2405 and contract NAS5-29298.