Dwarf novae in outburst : monitoring WX Hydri with IUE.

Abstract

An account is given of the monitoring of WX Hydri with the International Ultraviolet Explorer (IUE) satellite. The data obtained at the beginning of an outburst show that the rise of the optical precedes that of the ultraviolet flux. Observations during quiescence, together with archival data, indicate that the ultraviolet continuum and line fluxes decrease steadily between outbursts. The implications of the observations are discussed for the theoretical models of dwarf nova outbursts. It is concluded that the variable mass transfer model can accommodate the observations, but difficulties arise for the disk instability model.