Eclipse Studies of the Dwarf Nova HT Cassiopeiae. II. White Dwarf and Accretion Disk

Abstract

The white dwarf and accretion disk in the dwarf nova HT Cas are investigated by means of the simultaneous UBVR light curve presented by Horne et al. (1991). A temperature of 14,000 +/- 1000 K and a distance of 125 +/- 8 pc for E(B - V) = 0.0 are found. A blackbody fit to the UBVR fluxes yields T(W) of 13,600 +/- 1000 K and D of 140 +/- 12 pc. These estimates are consistent with the distance calculated from the near-IR spectrum of the M5.4 companion star by Marsh (1990). Eclipses are used to map the quiescent accretion disk. Maps of the disk at UBVR are derived on the basis of the mean of 12 light curves obtained in November-December 1983. These maps show that the quiescent disk in HT Cas has a flat brightness temperature profile (5000-7000 K), similar to the present white-light eclipse maps of Z Cha and OY Car. The multicolor data available for HT Cas show that the disk emission is characteristic of a partially ionized, optically thin gas.