How plasma coupling and convective-zone depth shape the rotation of solar-mass stars

TL;DR

This study explores how the depth of convective zones and plasma coupling influence the rotation rates of solar-mass stars, revealing a joint effect during early main-sequence stages.

Contribution

It introduces a combined convective coupling index linking internal stellar structure and plasma properties to rotation, highlighting their joint role in angular momentum regulation.

Findings

Weak individual correlations between rotation and either convective zone depth or plasma coupling.

Moderate correlation during early main-sequence when both factors are combined.

Diminished correlations in older stars, with thermodynamic effects becoming more prominent.

Abstract

Stellar rotation on the main sequence is a complex function of mass and age, displaying multiple regimes whose physical origin remains only partially understood. In particular, the connection between the diversity of observed rotation rates and the internal structure and thermodynamic properties of stellar interiors is still unclear. We investigated how the depth of the convective zones and the degree of plasma coupling, quantified through the plasma coupling parameter, relate to the observed rotation rates of solar-mass stars. We used a grid of $1 \, M_\odot$ MESA stellar models with a wide range of metallicities to identify the best-matching models for 243 main-sequence stars with measured rotation periods. We then examined correlations between their rotation rates and both the structural properties of the convective zones and the corresponding convective plasma coupling parameter. For this sample, rotation rates show only weak correlations with either the convective-zone depth or the plasma coupling parameter when considered independently. However, during the first two-thirds of the main-sequence lifetime, the correlation strengthens when both factors are considered jointly through a combined convective coupling index, indicating a moderate and statistically significant relationship. For older stars, these correlations weaken and lose significance, although the thermodynamic component becomes relatively more influential. These trends suggest that microphysical plasma properties may contribute to the regulation of angular momentum loss and may be connected to the onset of weakened magnetic braking.