VY Sculptoris stars as magnetic cataclysmic variables

¹ UMR 7550 du CNRS, Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: hameury@astro.u-strasbg.fr
² UMR 7095 du CNRS, Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France e-mail: lasota@iap.fr

Corresponding author: J.-M. Hameury, hameury@astro.u-strasbg.fr

Received: 14 May 2002
Accepted: 30 July 2002

Abstract

We show that the absence of outbursts during low states of VY Scl stars is easily explained if white dwarfs in these systems are weakly magnetized ( G cm³). However, some of the VY Scl stars are observed to have very slow declines to minimum and similarly slow rises to maximum. The absence of outbursts during such intermediate (as opposed to low) states, which last much longer than typical disc viscous times, can be explained only if accretion discs are absent when their temperatures would correspond to an unstable state. This requires magnetic fields stronger than those explaining outburst absence during low states, since white dwarfs in this sub-class of VY Scl stars should have magnetic moments  G cm³ i.e. similar to those of Intermediate Polars. Since at maximum brightness several VY Scl stars are SW Sex stars, this conclusion is in agreement with recent claims about the magnetic nature of these systems.