The EUV Spectrum of the Quasi-Coherent Oscillations of the Dwarf Nova SS Cygni

Abstract

Data obtained by the Extreme Ultraviolet Explorer satellite are used to determine the EUV spectrum of the quasi-coherent oscillations of the dwarf nova SS Cygni. It is found that the spectrum of the oscillations is neither blue nor red nor grey relative to the net (oscillation-phase integrated) spectrum, and hence that the oscillations cannot be explained by variations in the effective temperature, absorbing column density, or effective area, respectively. Instead, it is found that the amplitude of the oscillations is high at the relative maxima of the net spectrum, and low to zero at the relative minima of the net spectrum. This behavior can be explained by either variations in the emission line flux atop a constant underlying continuum, or variations in the optical depth of a haze of overlapping absorption lines, in which case the optical depths must be $τ<1$ at the relative maxima of the net spectrum, and $τ\gg 1$ at the relative minima.