Observations of the Dwarf Nova VW Hydri in Quiescence with the Hopkins Ultraviolet Telescope

Abstract

The dwarf nova VW Hydri was in quiescence when it was observed in 1995 March with the Hopkins Ultraviolet Telescope on the Astro-2 space shuttle mission. The far-UV (820-1840 Å) spectra are punctuated by broad Lyα and Lyβ absorption profiles and narrow absorption lines which can be identified with transitions expected in the atmosphere of a moderate-temperature white dwarf. There is no detectable emission shortward of 980 Å. The only emission line seen is C IV λλ1548, 1551. If the emission from VW Hyi is due to a uniform-temperature white dwarf; then our spectra suggest that the temperature of the white dwarf was ∼17,000 K at the time of our observations and that abundances in the atmosphere were subsolar. Improved fits to the data are obtained using models in which the far-UV emission arises in part from a white dwarf with near-solar abundances and in part from the accretion disk. However, given the uncertainties in model spectra of metal-enriched atmospheres in this temperature range and our limited knowledge of quiescent accretion disks, higher S/N spectra are needed to unambiguously assess the disk contribution to the far-UV spectrum of VW Hyi in quiescence.