Temporal variations of the white dwarf and disk in OY carinae following the 1992 superoutburst

Hubble Space Telescope observations of the eclipsing dwarf nova OY Carinae after its 1992 April superoutburst are used to isolate ultraviolet spectra (1150-2500 Angstrom at 9.2 Angstrom FWHM resolution) of the white dwarf, th e accretion disk, and the bright spot. The white dwarf spectra have a Stark -broadened photospheric Ly alpha absorption feature but are veiled by a for est of absorption features that we attribute to absorption by intervening d isk material (a curtain). All the spectral fits required supersonic turbule nce in the curtain material with Mach numbers of 6-8. All curtain temperatu res were between 10,000 and 11,000 K. There was a curtain temperature incre ase similar to 3 months after the superoutburst. We find that the white dwa rf temperature changed from 19,700 K just 27 days after the end of the supe routburst to 18,000 K roughly 3 months after the superoutburst; the exponen tial (e-folding) decay time of the white dwarf temperature was 66 days. We present evidence that the heating of the white dwarf was more extensive dur ing the superoutburst than the normal outburst. The thermal response of the OY Car white dwarf to outburst heating is compared with WZ Sagittae, VW Hy dri (the most similar dwarf nova to OY Car), and the cooling timescales of other dwarf novae after superoutburst. The measured cooling timescales of t he five systems with superoutbursts appear to be shorter the longer the orb ital period (accretion rate). Possible implications are discussed. There is evidence of a disk flux variation, independent of the effect of white dwar f cooling, which suggests a possible contradiction of the disk instability model. To establish this, however, data are required throughout a quiescent cycle.