A Boundary Layer Origin for Dwarf Nova Oscillations

Dwarf nova oscillations (DNOs) have been observed in a number of cataclysmic variables. I propose that these oscillations could be produced by a non-axisymmetric bulge at the transition between the optically thick disk and the optically thin boundary layer region. This would naturally explain the observed oscillation periods and the dependence of the oscillation amplitude on photon energy. The transition radius moves inward and outward with changing mass accretion rate, which explains the correlation between period and ux, and the timescale for period variations. The underlying cause of the non-axisymmetry which produces the oscillations is not known, so it is not possible to predict the oscillation amplitude from rst principles.