1996A&A...306..151B

The SU UMa type dwarf nova OY Car was observed in UBV and white light during its April 1992 superoutburst. The light curves show superhumps with a period of 0.06454d, consistent with previous observations. The structure of the superhump varies from night to night and is also wavelength-dependent. Maximum-entropy eclipse mapping techniques are used to obtain maps of the surface brightness distribution of the accretion disk. The disk maps show structures in their outer parts which can be interpreted as the superhump light source. They are compatible with theoretical predictions and recent modelling of the superhumps. They persist until two nights before the end of the superoutburst, while during the last night the bright spot of OY Car reappears at a location which suggests that the disk has shrunken below its quiescent radius. A two-color diagram of the pixels of the reconstructed disk shows that the inner disk is optically thick, with colors in between the blackbody and main sequence relationships. The angular scale of the disk and the distance to OY Car are estimated from a color-magnitude diagram by a method similar to cluster main-sequence fitting. We fit the Barnes-Evans relation to the pixels in the inner disk to find a distance of 86±4pc. Temperatures in the disk range from ∼6000K in the outer regions to ∼25000K near the white dwarf at disk centre and closely follow the T∝R^–3/4 law for steady mass accretion at a rate of {dot}(M)=10^{–9.20±0.08}M_☉/year. The evolution of the temperature distribution during the decline from the superoutburst reveals the existence of a cooling front in the disk which slowly propagates inward.