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

¹ European Space Astronomy Centre, SRE-O, PO Box 78, 28691 Villanueva de la Cañada, Madrid Spain
e-mail: Erik.Kuulkers@esa.int
² American Association of Variable Star Observers, 49 Bay State Rd., Cambridge, MA 02138, USA
³ Astronomy Department, Indiana University, Swain Hall West 319, 727 East 3rd Street, Bloomington, IN 47405-7105, USA
⁴ TMT Observatory Corporation, 2632 E Washington Blvd, Pasadena, CA 91107, USA
⁵ Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK

Received: 27 January 2010
Accepted: 22 January 2011

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.