Rotational evolution of young-to-old stars with data-driven three-dimensional wind models

Abstract

ABSTRACT Solar-type stars form with a wide range of rotation rates Ω. A wide Ω range persists until a stellar age of t ∼ 0.6 Gyr, after which solar-type stars exhibit Skumanich spin-down where Ω ∝ t−1/2. Rotational evolution models incorporating polytropic stellar winds struggle to simultaneously reproduce these two regimes, namely the initially wide Ω range and the Skumanich spin-down without imposing an a priori cap on the wind mass-loss rate. We show that a three-dimensional wind model driven by Alfvén waves and observational data yields wind torques that agree with the observed age distribution of Ω. In our models of the Sun and 27 open cluster stars aged from 0.04 to 0.6 Gyr that have observationally derived surface magnetic maps and rotation rates, we find evidence of exponential spin-down in young stars that are rapid rotators and Skumanich spin-down for slow rotators. The two spin-down regimes emerge naturally from our data-driven models. Our modelling suggests that the observed age distribution of stellar rotation rates Ω arises as a consequence of magnetic field strength saturation in rapid rotators.