Dwarf Nova Oscillations: New Results

Abstract

New and archived observations of VW Hyi in outburst show the occasional presence of optical Dwarf Nova Oscillations (DNOs) over the range of 18 - 40 s. There is a rapid increase in period near the end of outburst, at the same time that the EUV falls almost to zero, which we attribute to propellering. The DNOs return to a shorter period after this phase, but are very incoherent. The DNOs show some modulation by the Quasi-Periodic Oscillations (QPOs) that are also occasionally present in the light curve. We interpret the QPOs as a prograde travelling wave in the inner disc, which obscures and/or reprocesses radiation from the central region. The model is applied to observations of OY Car and WZ Sge.