Ultraviolet and optical observations of the dwarf novae VW and WX Hydri during outburst.
Schwarzenberg-Czerny, A.; Pringle, J. E.; Wade, R. A.; Hassall, B. J. M.; Whelan, J. A. J.; Hill, P. W.
United Kingdom
Abstract
Simultaneous spectrophotometry is presented in the range 1200-7000 A of the dwarf novae, at quiescence and maximum. The continuum spectra are compared with the standard model disk spectrum and, with one exception, the fit is poor. The assumptions that the disk is both steady-state and blackbody are reconsidered, and it is pointed out that a nu to the 1/3-power spectrum is not to be expected from a disk sufficiently small to be accommodated within these short binary period systems. On the rise to outburst, the UV flux in VW Hydri is observed to lag at least one day behind the optical, supporting the mass accretion event explanation of dwarf nova outbursts. The behavior of the UV and optical line features during outburst is described, in particular, the P Cygni features observed in a superoutburst of WX Hydri, from which a mass loss rate is estimated that is small, compared with the mass transfer rate from the secondary star.