The Coronal Structure of AB Doradus

TL;DR

This study uses MHD simulations driven by Zeeman-Doppler Imaging to analyze the complex coronal magnetic structure of AB Doradus, revealing higher mass and angular momentum loss rates compared to the Sun.

Contribution

It introduces a comprehensive MHD modeling approach to simulate the stellar corona of AB Doradus based on observed magnetic field maps, improving upon potential field extrapolation methods.

Findings

Coronal magnetic fields are strongly azimuthally tangled due to rapid rotation.

Mass loss rates are 10 to 500 times higher than the solar value.

Angular momentum loss can be up to 30,000 times greater than the Sun.

Abstract

We perform a numerical simulation of the corona of the young, rapidly rotating K0 dwarf AB Doradus using a global MHD model. The model is driven by a surface map of the radial magnetic field constructed using Zeeman-Doppler Imaging. We find that the global structure of the stellar corona is dominated by strong azimuthal tangling of the magnetic field due to the rapid rotation. The MHD solution enables us to calculate realistic Alfv\'en surfaces and we can therefore estimate the stellar mass loss rate and angular momentum loss rate without making undue theoretical simplifications. We consider three cases, parametrized by the base density of the corona, that span the range of possible solutions for the system. We find that overall, the mass and angular-momentum loss rates are higher than in the solar case; the mass loss rates are 10 to 500 times higher, and the angular momentum loss rate can be up to $3\times{10}^4$ higher than present day solar values. Our simulations show that this model can be use to constrain the wide parameter space of stellar systems. It also shows that an MHD approach can provide more information about the physical system over the commonly used potential field extrapolation.