The Search for SW Sex Type Stars

TL;DR

This study investigates the prevalence of SW Sex stars among non-eclipsing cataclysmic variables in the 2.8-4 hour period range, suggesting it is a common evolutionary stage in their development.

Contribution

It provides the first large spectroscopic survey confirming the dominance of SW Sex stars in this period range and proposes their evolutionary significance.

Findings

14 out of 18 stars are SW Sex type

High prevalence of SW Sex stars above the period gap

Supports SW Sex as an evolutionary stage

Abstract

All eclipsing nova-likes in the 2.8-4h orbital period range belong to the group of SW Sex stars, and as such experience very high mass transfer rates. Since the physical properties of a star should be independent of the inclination it is observed at, this suggests that all or at least a large fraction of the non- or weakly-magnetic cataclysmic variables in this period range are physically SW Sex stars. We here present preliminary results of a large campaign to search for SW Sex characteristic features in the spectra of such stars. We find that 14 out of the 18 observed non-eclipsing cataclysmic variables belong to the group of SW Sex stars the classification of the other four is uncertain from our data. This confirms the domination of SW Sex stars in the period range of 2.8-4 h just above the period gap. Since all long-period systems need to cross this range before entering the gap, the SW Sex phenomenon is likely to be an evolutionary stage in the life of a cataclysmic variable.