Characterising high and low accretion states in VY Scl CVs using ZTF and TESS data

TL;DR

This study analyzes ZTF and TESS data to characterize the high and low accretion states of VY Scl cataclysmic variables, revealing their state durations, transitions, and potential periodicities.

Contribution

It provides the first detailed analysis of state durations, transitions, and periodicities in VY Scl systems using combined ZTF and TESS observations.

Findings

Half of the systems spend most of their time in high states.

Identified a series of increasing brightness outbursts in KR Aur.

Detected a variable period between 3-6 days in LN UMa.

Abstract

VY Scl binaries are a sub-class of cataclysmic variable (CV) which show extended low states, but do not show outbursts which are seen in other classes of CV. To better determine how often these systems spend in low states and to resolve the state transitions we have analysed ZTF data on eight systems and TESS data on six systems. Half of the sample spent most of the time in a high state; three show a broad range and one spends roughly half the time transitioning between high and low states. Using the ZTF data we explore the colour variation as a function of brightness. In KR Aur, we identify a series of repeating outburst events whose brightness appears to increase over time. Using TESS data we searched for periods other than the orbital. In LN UMa we find evidence for a peak whose period varies between 3-6 d. We outline the current models which aim to explain the observed properties of VY Scl systems which includes disc irradiation and a white dwarf having a significant magnetic field.