The winds of young Solar-type stars in Coma Berenices and Hercules-Lyra

TL;DR

This study models stellar winds of young Solar-type stars in two clusters, revealing diverse wind geometries, significant variations in angular momentum and mass loss, and a strong correlation between magnetic flux and wind properties.

Contribution

It provides a comprehensive atlas of 15 observationally based wind models, highlighting the impact of magnetic field geometry on stellar wind characteristics and angular momentum loss.

Findings

Varied wind geometries and multi-armed structures observed.

Significant variation in angular momentum and mass loss rates.

Strong correlation between open magnetic flux and angular momentum loss.

Abstract

We present wind models of ten young Solar-type stars in the Hercules-Lyra association and the Coma Berenices cluster aged around 0.26 Gyr and 0.58 Gyr respectively. Combined with five previously modelled stars in the Hyades cluster, aged 0.63 Gyr, we obtain a large atlas of fifteen observationally based wind models. We find varied geometries, multi-armed structures in the equatorial plane, and a greater spread in quantities such as the angular momentum loss. In our models we infer variation of a factor of ~6 in wind angular momentum loss $\dot J$ and a factor of ~2 in wind mass loss $\dot M$ based on magnetic field geometry differences when adjusting for the unsigned surface magnetic flux. We observe a large variation factor of ~4 in wind pressure for an Earth-like planet; we attribute this to variations in the 'magnetic inclination' of the magnetic dipole axis with respect to the stellar axis of rotation. Within our models, we observe a tight correlation between unsigned open magnetic flux and angular momentum loss. To account for possible underreporting of the observed magnetic field strength we investigate a second series of wind models where the magnetic field has been scaled by a factor of 5. This gives $\dot M \propto B^{0.4}$ and $\dot J \propto B^{1.0}$ as a result of pure magnetic scaling.