Physical Parameter Eclipse Mapping of the quiescent disc in V2051 Ophiuchi

Abstract

We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has temperatures of 9000 K to 6500 K. The quiescent disc (chromosphere) shows a prominent bright region with temperatures of 10500 K around the impact region of the stream from the secondary with an extension towards smaller azimuths. The disc has a size of 0.53 +- 0.03 R_L1 and a mass accretion rate of between dM/dt = 10^15 g/s to 10^17g/s. The light curves must include an uneclipsed component, a hot chromosphere and/or a disc wind. The PPEM method allows us to determine a new distance of 146+-20pc, compatible with previous rough estimates. For the white dwarf we then reconstruct a temperature of 19600 K, if the lower hemisphere of the white dwarf is occulted by the disc. We find that although V2051 Oph is very similar to the SU UMa type dwarf novae HT Cas, OY Car and Z Cha, there must be a substantial difference in order to explain its unique light curve. For further details and results see paper.