The impact of metallicity on the evolution of the rotation and magnetic activity of Sun-like stars

Abstract

The rotation rates and magnetic activity of Sun-like and low-mass (.1.4M) main-sequence stars are knownto decline with time, and there now exist several models for the evolution of rotation and activity. However,the role that chemical composition plays during stellar spin-down has not yet been explored. In this work,we use a structural evolution code to compute the rotational evolution of stars with three different masses (0.7, 1.0, and 1.3M) and six different metallicities, ranging from [Fe/H]=−1.0 to [Fe/H]= +0.5. We also implement three different wind-braking formulations from the literature (two modern and one classical) and compare their predictions for rotational evolution. The effect that metallicity has on stellar structural properties,and in particular the convective turnover timescale, leads the two modern wind-braking formulations to predict a strong dependence of the torque on metallicity. Consequently, they predict that metal rich stars spin-down more effectively at late ages (>1 Gyr) than metal poor stars, and the effect is large enough to be detectable with current observing facilities. For example, the formulations predict that a Sun-like (solar-mass and solar-aged) star with [Fe/H]=−0.3 will have a rotation period of less than 20 days. Even though old, metal poor stars are predicted to rotate more rapidly at a given age, they have larger Rossby numbers and are thus expected to have lower magnetic activity levels. Finally, the different wind-braking formulations predict quantitative differences in the metallicity-dependence of stellar rotation, which may be used to test them