Giant coronal loops dominate the quiescent X-ray emission in rapidly rotating M stars

TL;DR

This study combines dynamo simulations and coronal modeling to show that large coronal loops, driven by strong magnetic fields, dominate the X-ray emission in rapidly rotating M stars, explaining their saturated X-ray levels.

Contribution

It introduces a physics-based model linking magnetic field structures to coronal X-ray emission, highlighting the dominance of large hot loops in rapidly rotating M stars.

Findings

Large-scale magnetic fields lead to dominant large hot coronal loops.

Coronal X-ray emission is primarily from star-sized large loops.

Small, colder loops contribute little to X-ray emission.

Abstract

Observations indicate that magnetic fields in rapidly rotating stars are very strong, on both small and large scales. What is the nature of the resulting corona? Here we seek to shed some light on this question. We use the results of an anelastic dynamo simulation of a rapidly rotating fully-convective M-star to drive a physics-based model for the stellar corona. We find that due to the several kilo Gauss large-scale magnetic fields at high latitudes, the corona and its X-ray emission are dominated by star-size large hot loops, while the smaller, underlying colder loops are not visible much in the X-ray. Based on this result we propose that, in rapidly rotating stars, emission from such coronal structures dominates the quiescent, cooler but saturated X-ray emission.