The dwarf nova dippers

Abstract

Two previous papers /1,2/ have shown that the dwarf nova OY Car has extensive vertical disc structure during its (~2 week) superoutbursts. This structure is analogous to that seen in the low mass X-ray binaries (LMXBs), in that the whole disc flares towards its edge, and there is a bulge or ``dark spot'' where the mass transfer stream meets the disc edge. In this paper we present evidence that two more dwarf novae may have such a stream impact bulge, which manifests itself as a dip in the UV light curve, analogous to those seen in the X-ray light curves of the LMXB dippers.