Magnetic Structure of Rapidly Rotating FK Comae-Type Coronae

TL;DR

This study uses 3D magnetohydrodynamic simulations driven by stellar dynamo models to reveal the complex magnetic and density structures of FK Com-type star coronae, highlighting differences from the solar corona.

Contribution

It introduces a novel 3D simulation approach for FK Com-type star coronae using surface magnetic maps, capturing non-potential magnetic structures and their effects.

Findings

Coronal magnetic field is dominated by a strong toroidal component.

Magnetic field tangling causes a flattened density profile in the inner corona.

Results suggest coronae of fast rotators differ significantly from the solar corona.

Abstract

We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field,in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular, should lead to an improved understanding of mass and angular momentum loss from such systems.