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

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.