Ultraviolet observations of cataclysmic variables

Abstract

The ultraviolet spectra of cataclysmic variables provide us with information on the mass transfer in these systems, and on the variations therein on different time scales. The combined ultraviolet and optical spectra cannot be fitted with simple model spectra, and accordingly, our interpretations of the observed spectra are subject to uncertainty. Nonetheless, useful constraints on theory have been obtained from observations of dwarf nova outbursts and of high and low states in AM Her type systems.

Ultraviolet resonance lines arising in remarkably dense winds are often seen in spectra of cataclysmic variables, in emission, in asymmetric absorption, or with P-Cygni profiles. Systems in which the white dwarf has a strong magnetic field, and systems with high inclination show pure emission profiles. Line profiles vary with the continuum level during dwarf nova outbursts. Pronounced orbital variations in the line profiles have been observed in a number of systems, indicating large asymmetries in the wind outflow geometry.