Age dependence of wind properties for solar type stars: a 3d study

TL;DR

This study uses 3D MHD simulations based on ZDI maps to analyze how wind properties and angular momentum loss in solar-type stars evolve with age, revealing saturation effects and complex wind structures in young stars.

Contribution

It introduces a detailed 3D simulation approach linking magnetic field maps to stellar wind evolution and angular momentum loss in young K-type stars, enhancing understanding of stellar spin-down.

Findings

Angular momentum loss decreases with ge, following the Skumanich law.

Signs of saturation in angular momentum loss at 8\u03a9_{\u00b0} for young stars.

Young stars exhibit complex wind speed distributions with multiple components.

Abstract

Young and rapidly rotating stars are known for intense, dynamo generated magnetic fields. Spectropolarimetric observations of those stars in precisely aged clusters are key input for gyrochronology and magnetochronology. We use ZDI maps of several young K-type stars of similar mass and radius but with various ages and rotational periods, to perform 3D numerical MHD simulations of their coronae and follow the evolution of their magnetic properties with age. Those simulations yield the coronal structure as well as the instant torque exerted by the magnetized, rotating wind on the star. As stars get older, we find that the angular momentum loss decreases with $\Omega^3$, which is the reason for the convergence on the Skumanich law. For the youngest stars of our sample, the angular momentum loss show signs of saturation around $8\Omega_{\odot}$, which is a common value used in spin evolution models for K-type stars. We compare these results to semi-analytical models and existing braking laws. We observe a complex wind speed distribution for the youngest stars with slow, intermediate and fast wind components, which are the result of the interaction with intense and non axisymmetric magnetic fields. Consequently, in our simulations, the stellar wind structure in the equatorial plane of young stars varies significantly from a solar configuration, delivering insight about the past of the solar system interplanetary medium.