Ultraviolet observations of cataclysmic variables : the IUE archive.

Abstract

A comparative study of the ultraviolet properties of cataclysmic variables is made on the basis of the IUE data archive. The reddening to 51 systems is determined from the 2200 Å feature. The spectral flux distribution of cataclysmic variables does not depend on system type, orbital period or (for dwarf novae) average length of interval between outburst maxima; it does not depend strongly on inclination. The exception is formed by the DQ Her systems, which may have relatively low fluxes at short wavelengths as compared to the other systems. All systems for which observations are available show variability on a time scale of hours. In two nova-like variables in a low state and in five dwarf novae in quiescence there is evidence that most of the ultraviolet flux at short wavelengths is due to the white dwarf. Disk model spectra are calculated to show that the slope of the spectrum depends strongly on the white dwarf mass. Hence determinations of the mass transfer rate from the spectral slope are subject to large errors in cases where the white dwarf mass is not known.