An active K0 IV-V star and a hot white dwarf (EUVE J0702+129) in a wide binary

We present far ultraviolet and optical spectroscopy of the Extreme Ultraviolet Explorer (EUVE) survey source EUVE J0702+129 revealing a composite K0 star plus DA white dwarf spectrum. The 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 greater than or equal to 2500 Angstrom. High resolution optical spectroscopy uncovers a high level of activity with strong H alpha and Ca 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 similar to 130 pc and they likely constitute a physical pair. The EUV emission is dominated by the white dwarf, but the late-type star certainly contributes at higher energy. An interesting parallel is 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).