Roche tomography of cataclysmic variables - VII. The long-term magnetic activity of AE Aqr

TL;DR

This long-term study uses Roche tomography to image starspots on AE Aqr over 8 years, revealing persistent high-latitude spots and potential magnetic activity cycles, providing insights into stellar magnetic behavior in close binaries.

Contribution

First long-term Roche tomography imaging of AE Aqr's starspots, revealing evolving high-latitude spots and magnetic activity patterns over 8 years.

Findings

Presence of persistent high-latitude starspots.

Growth in spot coverage around 45° latitude.

Evidence of magnetic activity cycles similar to the solar butterfly diagram.

Abstract

We present a long-term study of the secondary star in the cataclysmic variable AE~Aqr, using Roche tomography to indirectly image starspots on the stellar surface spanning 8~years of observations. The 7 maps show an abundance of spot features at both high and low latitudes. We find that all maps have at least one large high-latitude spot region, and we discuss its complex evolution between maps, as well as its compatibility with current dynamo theories. Furthermore, we see the apparent growth in fractional spot coverage, $f_{\mathrm{s}}$, around $45^{\circ}$~latitude over the duration of observations, with a persistently high $f_{\mathrm{s}}$ near latitudes of $20^{\circ}$. These bands of spots may form as part of a magnetic activity cycle, with magnetic flux tubes emerging at different latitudes, similar to the `butterfly' diagram for the Sun. We discuss the nature of flux tube emergence in close binaries, as well as the activity of AE~Aqr in the context of other stars.