Radio masers on WX UMa: hints of a Neptune-sized planet, or magnetospheric reconnection?

Robert D Kavanagh*, Aline A Vidotto, Harish K Vedantham, Moira M Jardine, Joe R Callingham, Julien Morin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
1 Downloads (Pure)


The nearby M dwarf WX UMa has recently been detected at radio wavelengths with LOFAR. The combination of its observed brightness temperature and circular polarisation fraction suggests that the emission is generated via the electron-cyclotron maser instability. Two distinct mechanisms have been proposed to power such emission from low-mass stars: either a sub-Alfvénic interaction between the stellar magnetic field and an orbiting planet, or reconnection at the edge of the stellar magnetosphere. In this paper, we investigate the feasibility of both mechanisms, utilising the information about the star’s surrounding plasma environment obtained from modelling its stellar wind. Using this information, we show that a Neptune-sized exoplanet with a magnetic field strength of 10 – 100 G orbiting at ∼0.034 au can accurately reproduce the observed radio emission from the star, with corresponding orbital periods of 7.4 days. Due to the stellar inclination, a planet in an equatorial orbit is unlikely to transit the star. While such a planet could induce radial velocity semi-amplitudes from 7 to 396 m s−1, it is unlikely that this signal could be detected with current techniques due to the activity of the host star. The application of our planet-induced radio emission model here illustrates its exciting potential as a new tool for identifying planet-hosting candidates from long-term radio monitoring. We also develop a model to investigate the reconnection-powered emission scenario. While this approach produces less favourable results than the planet-induced scenario, it nevertheless serves as a potential alternative emission mechanism which is worth exploring further.
Original languageEnglish
Article numberstac1264
Pages (from-to)675–688
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date10 May 2022
Publication statusPublished - 1 Jul 2022


  • Stars: individual: WX UMa
  • Stars: winds
  • Stars: mass-loss
  • Stars: magnetic field
  • Radio continuum: planetary systems
  • Outflows


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