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

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1. Binaries in the EUV-selected white dwarf population

Recent extreme ultraviolet (EUV) all-sky surveys (EUVE, Bowyer et al. 1996; ROSAT WFC, Pye et al. 1995) revealed several new white dwarfs paired with a luminous secondary star. Landsman, Simon, & Bergeron (1993) and Vennes et al. (1995) report on two hydrogen-rich (DA) white dwarfs (EUVE J0459-102 and EUVE J0254-053) associated with the bright K0 IV stars HR 1608 and HD 18131. Both systems, comprising an evolved secondary, may help constrain initial-to-final-mass relations for white dwarf stars. Very little is known of the secondary stars themselves, and further studies should be aimed at identifying intrinsic properties such as the level of activity, rotation period, and abundance; we need to search for evidence of past interaction with the post-AGB primary. Kellet et al. (1995) found possible evidence of such interactions in the fast rotating secondary star of the K0V+DA binary [FORMULA]. Jeffries, Burleigh, & Robb (1996) uncovered similar behavior in the K2V star 2RE J0357+283; Jeffries & Stevens (1996) theorize that accretion from the red giant wind may possibly increase the rotational velocity of the secondary star up to [FORMULA].

We initiated a systematic survey of EUV-selected G and K stars at ultraviolet wavelengths using the International Ultraviolet Explorer (IUE). We present in § 2 our far ultraviolet (FUV) spectra and discovery of a new DA white dwarf, and we present high- and low-dispersion optical spectroscopy of the secondary star. We discuss the properties of the white dwarf in § 3, and some characteristics of the binary and its secondary star in § 4.

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998