Secular changes in the quiescence of WZ Sge: the development of a cavity in the inner disk

TL;DR

This paper reports a decade-long dimming in WZ Sge's optical quiescence linked to the formation of an inner disk cavity, supporting a magnetic propeller model where the white dwarf expels accreting material during quiescence.

Contribution

It provides evidence for a cavity development in the accretion disk of WZ Sge and connects it to magnetic field effects, advancing understanding of quiescent phases in cataclysmic variables.

Findings

Dimming of about half a magnitude during quiescence.

Development of a cavity in the inner accretion disk over about a decade.

Support for the magnetic propeller model in explaining mass expulsion.

Abstract

We find a dimming during optical quiescence of the cataclysmic variable WZ Sge by about half a magnitude between superoutbursts. We connect the dimming with the development of a cavity in the inner part of the accretion disk. We suggest that, when the cavity is big enough, accretion of material is governed by the magnetic field of the white dwarf and pulsations from the weakly magnetic white dwarf appear. The time scale of forming the cavity is about a decade, and it persists throughout the whole quiescent phase. Such a cavity can be accommodated well by the proposed magnetic propeller model for WZ Sge, where during quiescence mass is being expelled by the magnetic white dwarf from the inner regions of the accretion disk to larger radii.