Large closed-field corona of WX UMa evidenced from radio observations

TL;DR

This study detects low-frequency radio emissions from WX UMa, revealing that its closed magnetic field regions extend significantly beyond the solar corona, indicating a magnetic structure intermediate between Sun-like and planet-like configurations.

Contribution

First detection of low-frequency radio emission from WX UMa, providing new insights into the extent and structure of its stellar corona and magnetic field.

Findings

Closed magnetic regions extend to at least 10 stellar radii.

Coronal magnetic structure is intermediate between Sun-like and planet-like.

Magnetic field configuration includes both dense loops and large-scale magnetosphere.

Abstract

The space-weather conditions that result from stellar winds significantly impact the habitability of exoplanets. The conditions can be calculated from first principles if the necessary boundary conditions -- namely on the plasma density in the outer corona and the radial distance at which the plasma forces the closed magnetic field into an open geometry -- are specified. Low frequency radio observations ($\nu \lesssim 200$ MHz) of plasma and cyclotron emission from stars probe these magneto-ionic conditions. Here we report the detection of low-frequency ($120-167\,{\rm MHz}$) radio emission associated with the dMe6 star WX UMa. If the emission originates in WX UMa's corona, we show that the closed field regions extends to at least $\approx 10$ stellar radii, that is about a factor of a few larger than the solar value, and possibly to $\gtrsim 20$ stellar radii. Our results suggest that the magnetic-field structure of M dwarfs is in between Sun-like and planet-like configurations, where compact over-dense coronal loops with X-ray emitting plasma co-exist with a large-scale magnetosphere with lower plasma density and closed magnetic geometry.