The accretion disk (belt?) during the quiescence of VW Hydri

We considered the contribution of an accretion disk to the UV spectrum of the dwarf nova (DN) VW Hydri during its quiescence, obtained with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). Our analysis indicates that the UV emitting area of the disk is a ring of width 0.06 R(WD), inclination angle i=60 degrees, rotating with Keplerian velocity on the white dwarf surface of 3350 km/s. The other parameters of the ring are log g=6.0, T-eff=28,000 K, C and Si enhanced to 20 and 15 times their solar abundances, respectively, and the abundance of all other heavy elements having solar values. The disk area outside this UV emitting region has a T-eff much lower than 10,000 K. Our modelling does not rule out that the ring could actually be a belt on the white dwarf. For the central while dwarf, our analysis yields a T-eff=22,000+/-1000 K, log g=8.0, with the abundance of all heavy elements 0.3 times their solar values. This disk contributes about 12% of the total far UV flux in the FOS far ultraviolet region. (C) 1996 American Institute of Physics.