OBSERVATIONS OF THE DWARF-NOVA-VW-HYDRI IN QUIESCENCE WITH THE HOPKINS-ULTRAVIOLET-TELESCOPE

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 shu ttle mission. The far-UV (820-1840 Angstrom) spectra are punctuated by broad Ly alpha and Ly beta absorption profiles and narrow absorption lines which can be identified with transitions expected in the atmosph ere of a moderate-temperature white dwarf. There is no detectable emis sion shortward of 980 Angstrom. The only emission line seen is C IV la mbda lambda 1548, 1551. If the emission from VW Hyi is due to a unifor m-temperature white dwarf, then our spectra suggest that the temperatu re of the white dwarf was similar to 17,000 K at the time of our obser vations and that abundances in the atmosphere were subsolar. Improved fits to the data are obtained using models in which the far-UV emissio n arises in part from a white dwarf with near-solar abundances and in part from the accretion disk. However, given the uncertainties in mode l 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-U V spectrum of VW Hyi in quiescence.