2010ApJ...716L.157S

We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer (FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. In our synthetic spectral analysis, we have used SS Cygni's accurate HST fine guidance sensor parallax giving d = 166 pc, a newly determined mass for the accreting white dwarf (WD) of M_wd= 0.81 M_☉(lower than the previous widely used 1.2 M_☉) and the reddening (E_B–V) values 0.04 and 0.07 derived from the 2175 Å absorption feature in the IUE LWP spectra. From the best-fit model solutions to the combined HST + FUSE spectral energy distribution, we find that the WD is reaching a temperature ≈ _eff≈ 45,000-55,000 K in quiescence, assuming log(g) = 8.3 with a solar composition accreted atmosphere. The exact temperature of the WD depends on the reddening assumed and the inclusion of a quiescent low mass accretion rate accretion disk. Accretion disk models alone fit badly in the FUSE range while, and if we take the distance to be a free parameter, the only accretion disk model that fits well is for a discordant distance of at least several hundred parsecs and an accretion rate (∼10^–8 M_☉/yr), which is unacceptably high for a dwarf nova in quiescence. We discuss the implications of the WD's temperature on the time-averaged accretion rate and long-term compressional heating models.