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Astron. Astrophys. 318, L9-L12 (1997)

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Letter to the Editor

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

S. Vennes 1, D.J. Christian 1, M. Mathioudakis 2 and J.G. Doyle 3

1 Center for EUV Astrophysics, 2150 Kittredge Street, University of California, Berkeley, CA 94720-5030, USA
2 Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Athens, GR-15783, Athens, Greece
3 Armagh Observatory, Armagh BT61 9DG, Ireland

Received 26 November 1996 / Accepted 13 December 1996

Abstract

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 ([FORMULA] K) and a rising contribution from the K0 star at [FORMULA] Å. High resolution optical spectroscopy uncovers a high level of activity with strong H [FORMULA] 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 [FORMULA] 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).

Key words: binaries: general – - Stars: chromospheres – - Stars: evolution – - white dwarfs – - Stars: individual: EUVE J0702+129

Send offprint requests to: S. Vennes

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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