Coherent radio emission from a quiescent red dwarf indicative of star–planet interaction

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Abstract

Low-frequency (ν 150 MHz) stellar radio emission is expected to originate in the outer corona at heights comparable to and larger than the stellar radius. Such emission from the Sun has been used to study coronal structure, mass ejections and space-weather conditions around the planets1. Searches for low-frequency emission from other stars have detected only a single active flare star2 that is not representative of the wider stellar population. Here we report the detection of low-frequency radio emission from a quiescent star, GJ 1151—a member of the most common stellar type (red dwarf or spectral class M) in the Galaxy. The characteristics of the emission are similar to those of planetary auroral emissions3 (for example, Jupiter’s decametric emission), suggesting a coronal structure dominated by a global magnetosphere with low plasma density. Our results show that large-scale currents that power radio aurorae operate over a vast range of mass and atmospheric composition, ranging from terrestrial planets to main-sequence stars. The Poynting flux required to produce the observed radio emission cannot be generated by GJ 1151’s slow rotation, but can originate in a sub-Alfvénic interaction of its magnetospheric plasma with a short-period exoplanet. The emission properties are consistent with theoretical expectations4,5,6,7 for interaction with an Earth-size planet in an approximately one- to five-day-long orbit.

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Fig. 1: Total intensity deconvolved images of the region around GJ 1151 for two different epochs.
Fig. 2: The variability of the flux density.
Fig. 3: A comparison of observationally inferred and theoretical values for the starward Poynting flux from sub-Alfvénic interaction with an Earth-size exoplanet.

Data availability

Source data for Fig. 2 are provided with the paper. The raw LOFAR data are available for download from the LOFAR long-term archive at https://lta.lofar.eu. GJ 1151 was detected in an exposure with observation i.d. L231631. Pre-calibrated and in-field source subtracted visibility data (about 50 GB) are available from the corresponding author upon reasonable request.

Code availability

The raw interferometric data were processed with publicly available packages (see ref. 8 for details). Custom scripts used in the star–planet interaction calculations/plots are available at https://github.com/harishved/GJ1151_SPI

Change history

  • 24 February 2020

    In the PDF version of this Letter originally published, the text in the penultimate paragraph of the main text, ‘with semi-amplitude of 4.3 × 1013 ergs s–­1 Hz–­1’, was incorrect; it should have read ‘with semi-amplitude of ~1 m s–1 × sini’. This has now been updated.

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Acknowledgements

H.K.V. and J.R.C. thank D. Melrose, A. Vidotto and P. Zarka for discussions. H.K.V. thanks V. Ravi and G. Hallinan for discussions. The Leiden LOFAR team gratefully acknowledge support from the European Research Council under the European Unions Seventh Framework Programme (FP/2007-2013)/ERC Advanced Grant NEWCLUSTERS-321271. I.S. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement number 694513. G.J.W. gratefully acknowledges support of an Emeritus Fellowship from The Leverhulme Trust. S.P.O. acknowledges financial support from the Deutsche Forschungsgemeinschaft (DFG) under grant BR2026/23. M.H. acknowledges funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 772663. This paper is based (in part) on data obtained with the International LOFAR Telescope (ILT). LOFAR is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing and data storage facilities in several countries, which are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefited from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK. This work was in part carried out on the Dutch national e-infrastructure with the support of the SURF Cooperative through grants e-infra 160022 and 160152. The LOFAR software and dedicated reduction packages on https://github.com/apmechev/GRID_LRT were deployed on these e-infrastructure by the LOFAR e-infragroup. This research has made use of data analysed using the University of Hertfordshire high-performance computing facility (http://uhhpc.herts.ac.uk/) and the LOFAR-UK computing facility located at the University of Hertfordshire and supported by STFC (ST/P000096/1). This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. B.J.S.P. acknowledges being on the traditional territory of the Lenape Nations and recognizes that Manhattan continues to be the home to many Algonkian peoples. We give blessings and thanks to the Lenape people and Lenape Nations in recognition that we are carrying out this work on their indigenous homelands.

Author information

H.K.V. and J.R.C. developed the detection strategy, cross-matched the optical and radio catalogues, and discovered the source. H.K.V. modelled the radio emission and wrote the manuscript. J.R.C. initiated the LOFAR project that led to the discovery of the source and contributed to the manuscript. T.W.S. processed the radio data with software developed by members of the LoTSS survey collaboration including C.T. and M.J.H. C.T. wrote the software to extract quick-look dynamic spectra. H.J.A.R. is the principal investigator of the broader LOFAR Two-Metre Sky Survey. All authors commented on the manuscript.

Correspondence to H. K. Vedantham.

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Extended data

Extended Data Fig. 1 Astrometric association of the radio source with the star GJ1151.

Relative astrometry of the radio source in GJ 1151 and the optical position of M-dwarf star GJ 1151. The optical position and proper-motion correction is based on the Gaia DR2 catalog. The error-bars show the ±1σ errors on the radio source centroid that were computed by adding the formal errors in source-finding and the absolute LoTSS astrometric uncertainty in quadrature.

Source data

Source Data Fig. 2

ASCII text file with the data plotted in Fig. 2. The first batch of data relates to panel a, the second batch relates to panel b. The column variable names and units are given in the first row of each batch.

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Vedantham, H.K., Callingham, J.R., Shimwell, T.W. et al. Coherent radio emission from a quiescent red dwarf indicative of star–planet interaction. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1011-9

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