Photometric variability as a proxy for magnetic activity and its dependence on metallicity

TL;DR

This study explores how metallicity influences magnetic activity in low-mass stars, revealing that higher metallicity correlates with increased photometric variability and affects rotation period detection biases.

Contribution

It demonstrates the metallicity dependence of photometric variability and its impact on magnetic activity proxies, extending understanding beyond the Rossby number's role.

Findings

Photometric variability amplitude is parameterized by the Rossby number.

Variability amplitude positively correlates with metallicity.

Metal-rich stars have more easily detectable rotation periods.

Abstract

Understanding how the magnetic activity of low-mass stars depends on their fundamental parameters is an important goal of stellar astrophysics. Previous studies show that activity levels are largely determined by the stellar Rossby number which is defined as the rotation period divided by the convective turnover time. However, we currently have little information on the role that chemical composition plays. In this work, we investigate how metallicity affects magnetic activity using photometric variability as an activity proxy. Similarly to other proxies, we demonstrate that the amplitude of photometric variability is well parameterised by the Rossby number, although in a more complex way. We also show that variability amplitude and metallicity are generally positively correlated. This trend can be understood in terms of the effect that metallicity has on stellar structure and, hence, the convective turnover time (or, equivalently, the Rossby number). Lastly, we demonstrate that the metallicity dependence of photometric variability results in a rotation period detection bias whereby the periods of metal-rich stars are more easily recovered for stars of a given mass.