The low states of CVs at the upper edge of the period gap

TL;DR

This paper reviews the low states of cataclysmic variables near the period gap, focusing on the elusive SW Sextantis stars, and presents initial findings on their component stars and accretion activity during low states.

Contribution

It provides the first characterization of white dwarfs and donor stars in VY Scl systems near the period gap during low states and reports new observations of sporadic accretion and magnetic activity.

Findings

Characterization of white dwarfs and donor stars in VY Scl systems during low states

Discovery of sporadic accretion events in these systems

Detection of satellite emission lines linked to magnetic activity

Abstract

We review our knowledge of the origin and phenomenology of low states (also known as VY Scl states) in cataclysmic variables, making special emphasis on the cataclysmic variable population found just above the period gap. This orbital period range between approximately 3 and 4 hours is the preferred land for the elusive SW Sextantis stars, which are believed to be about to enter the gap when their donor stars become fully convective. Despite their main role in our understanding of the whole picture of cataclysmic variable evolution, the study of their component stars is almost impossible due to the extreme veiling brightness of the accretion disc during the high state. Here we present the first steps toward the characterisation of the white dwarfs and the donor stars in these VY Scl systems in the low state, and the discovery of sporadic accretion events and satellite emission lines like those observed in the AM Her systems in the low state, which are likely related to magnetic activity of the fast rotating secondary stars.