Angular Momentum Transport In Solar-Type Stars: Testing the Timescale For Core-Envelope Coupling

TL;DR

This paper investigates the internal angular momentum transport in solar-type stars, testing different models against observed rotation distributions in star clusters, and finds that core-envelope decoupling models best explain the data.

Contribution

It provides new constraints on core-envelope coupling timescales in solar-type stars and challenges the applicability of the Tayler-Spruit magnetic transport mechanism for these stars.

Findings

Solid body models fit low-mass stars but not higher mass stars.

Core-envelope decoupling models explain observed spin-down with specific timescales.

Transport timescales are shorter for rapidly rotating stars.

Abstract

We critically examine the constraints on internal angular momentum transport which can be inferred from the spin down of open cluster stars. The rotation distribution inferred from rotation velocities and periods are consistent for larger and more recent samples, but smaller samples of rotation periods appear biased relative to vsini studies. We therefore focus on whether the rotation period distributions observed in star forming regions can be evolved into the observed ones in the Pleiades, NGC2516, M34, M35, M37, and M50 with plausible assumptions about star-disk coupling and angular momentum loss from magnetized solar-like winds. Solid body models are consistent with the data for low mass fully convective stars but highly inconsistent for higher mass stars where the surface convection zone can decouple for angular momentum purposes from the radiative interior. The Tayler-Spruit magnetic angular momentum transport mechanism, commonly employed in models of high mass stars, predicts solid-body rotation on extremely short timescales and is therefore unlikely to operate in solar-type pre-MS and MS stars at the predicted rate. Models with core-envelope decoupling can explain the spin down of 1.0 and 0.8 solar mass slow rotators with characteristic coupling timescales of 55+-25 Myr and 175+-25 Myr respectively. The upper envelope of the rotation distribution is more strongly coupled than the lower envelope of the rotation distribution, in accord with theoretical predictions that the angular momentum transport timescale should be shorter for more rapidly rotating stars. Constraints imposed by the solar rotation curve are also discussed (Abridged)