Rapid light variations of YZ Cancri: An unusual SS Cygni star

High time-resolution photometry of the 55 Cygni variable YZ Cancri is reported. A thorough search for photometric evidence of binary effects is negative. In the light of previous spectroscopy, this is interpreted as evidence for a small inclination of the orbit to the plane of the sky. Incoherent light variation ("flickering") is observed down to a time scale of 20 s. The extraordinary amplitude of the flickering, 0.75 mag peak-to-peak, demands that the hot spot dominate the light from the system, which probably indicates a high rate of mass transfer. There is marginal evidence for coherent oscillation with a period of 27 s and amplitude of 0.0018 mag during the decline from maximum light (outburst). Subject heading: binaries - dwarf novae - pulsation - stars, individual - U Geminorum stars