paper

Rotational evolution of slow-rotators sequence stars

arXiv:1506.05298 · doi:10.1051/0004-6361/201526770

Abstract

The observed mass-age-rotation relationship in open clusters shows the progressive development of a slow-rotators sequence. The observed clustering on this sequence suggests that it corresponds to some equilibrium or asymptotic condition that still lacks a complete theoretical interpretation, crucial to our understanding of the stellar angular momentum evolution. We couple a rotational evolution model, which takes into account internal differential rotation, with classical and new proposals for the wind braking law, and fit models to the data using a MCMC method. The description of the evolution of the slow-rotators sequence requires taking into account the transfer of angular momentum from the radiative core to the convective envelope; we find that, in the mass range 0.85-1.10 , the core-envelope coupling time-scale for stars in the slow-rotators sequence scales as . Quasi-solid body rotation is achieved only after 1-2 Gyr, depending on stellar mass, which implies that observing small deviations from the Skumanich law () would require period data of older open clusters than available to date. The observed evolution in the 0.1-2.5 Gyr age range and in the 0.85-1.10 mass range is best reproduced by assuming an empirical mass dependence of the wind angular momentum loss proportional to the convective turnover time-scale and to the stellar moment of inertia. Period isochrones based on our MCMC fit provide a tool for inferring stellar ages of solar-like main-sequence stars from their mass and rotation period largely independent from the wind braking model adopted. These effectively represent gyro-chronology relationships that take into account the physics of the two-zone model for the stellar angular momentum evolution.

16 pages, 8 figures, 4 tables, accepted by A&A

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