On a stochastic model for the spin-down of solar type stars

Abstract

Modeling the rotation history of solar-type stars is still an unsolved problem in modern astrophysics. One of the main challenges is to explain the dispersion in the distribution of stellar rotation rate for young stars. Previous works have advocated dynamo saturation or magnetic field localization to explain the presence of fast rotators and star-disk coupling in pre-main sequence to account for the existence of slow rotators. Here, we present a new model that can account for the presence of both types of rotators by incorporating fluctuations in the solar wind. This renders the spin-down problem probabilistic in nature, some stars experiencing more braking on average than others. We show that random fluctuations in the loss of angular momentum enhance the population of both fast and slow rotators compared to the deterministic case. Furthermore, the distribution of rotational speed is severely skewed towards large values in agreement with observations