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

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 ($120-167\mathrm{MHz}$) 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.

arXiv commentAccepted for publication in A&A, 10 pages, 7 figures, 2 tables

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• V-LoTSS: The Circularly-Polarised LOFAR Two-metre Sky Survey
• The TESS View of LOFAR Radio-Emitting Stars
• Radio masers on WX UMa: hints of a Neptune-sized planet, or magnetospheric reconnection?
• Peculiar radio$-$X-ray relationship in active stars
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• Testing a scaling relation between coherent radio emission and physical parameters of hot magnetic stars
• Star-Planet Interactions: A Computational View
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• Extended scenarios for solar radio emissions with downshifted electron beam plasma excitations
• Radio emission from flaring stars and brown dwarfs