A photometric study of the dwarf nova WZ Sagittae in outburst

Abstract

Periodic light curve humps are seen at all times in high-speed photometry results of WZ Sagittae during its 1978 eruption, with a variation at the orbital period appearing to be present throughout the eruption. If this variation arises from a mass-transfer bright spot, then the spot must have migrated about 60 deg downstream at maximum light from its position at quiescence. A more prominent modulation, or superhump, appeared with a period 0.8% greater than the orbital period during the latter part of the eruption. The star is identified as an SU UMa-type dwarf nova, whose light curves are in fair agreement with predictions of the mass-transfer instability theory, but not easily explainable if the instability originates from the accretion disk or the white dwarf. The periodic humps suggest that enhanced mass transfer from the secondary occurred throughout the eruption, producing at least 30% of its visual luminosity.