ON THE X-RAY EMITTING BOUNDARY-LAYER OF THE DWARF NOVA VW-HYDRI

By combining EXOSAT LE filter observations of the dwarf nova VW Hyi in superoutburst with Voyager far-and extreme-ultraviolet spectrophotometry and a measurement of the column density of neutral hydrogen, we have constrained the temperature and luminosity of the boundary layer of VW Hyi to be kT(BL) approximately 10.5 eV and L(BL) approximately 6 x 10(32) (d/65 pc)2 ergs s-1. Based on contemporaneous optical, IUE, and Voyager spectrophotometry, Polidan, Mauche, & Wade found that the luminosity of the accretion disk is L(disk) approximately 1.5 x 10(34) (d/65 pc)2 ergs s-1. Therefore, while theory predicts that the luminosities of the boundary layer and the accretion disk should be comparable unless the white dwarf is rotating very rapidly, zeta = L(BL)L(disk) approximately 1, we find that zeta approximately 0.04. We also find that EXOSAT Al-Par filter observations of VW Hyi in outburst are likely to be severely contaminated by light from the accretion disk. The contamination of the Al-Par filter and the consequent high Al-Par over 3000 Lex filter ratio is therefore not the signature of a luminous ultrasoft boundary layer but rather that of the inner accretion disk, a component which is suppressed in observations of other cataclysmic variables because of their higher neutral hydrogen column densities.