V2051 Oph's disc evolution on decline from superoutburst

Abstract

We present an Eclipse Mapping analysis of ten eclipses taken during decline from superoutburst of the dwarf nova V2051 Oph. On decline from superoutburst the disc cools down considerably from nearly 50,000 K in the intermediate disc (approx. 0.2 R_L1) near maximum to about 25,000 K at the end of our observing run, i.e. within 4 days. The average mass accretion rate through the disc drops in the same time from 10^18 g/s to below 10^17 g/s. While in some maps the brightness temperature follows the steady state model, in others the temperature profile shows flattenings and/or indication of an inward travelling cooling front with a speed of approximately -0.12 km/s, possibly a reflected heating front with a speed of +1.8 km/s and a newly reflected cooling front with the same speed as the first one. Such scenario has been predicted (Menou et al. 2000) but not been observed before. Furthermore, we see a prograde precession of the enlarged disc with a precession period of about 52.5 hours in very good agreement with the independently determined superhump period observed by Kiyota & Kato (1998). At the same time, the uneclipsed component -- presumeably a disc wind -- decreases significantly in strength during decline from superoutburst.