Dwarf nova outbursts - the ultraviolet delay and the effect of a weakly magnetized white dwarf

Abstract

We investigate the effect on the properties of the outbursts of a dwarf nova (in the disk instability model) of the central white dwarf having a weak (about 10,000 G) magnetic field. We find that in quiescence the inner regions of the disk are evacuated by the presence of the field. This implies that at the beginning of the outburst there is a delay before the hotter inner disk regions are filled and radiating, and thus the optical flux can rise 12 h or so before the ultraviolet flux. During outburst the effect of the field on the disk is negligible. Thus the presence of such a weak field would be hard to detect directly by, for example, looking for coherent pulsations in the emitted light.