Coherent low-frequency (≲200 MHz) radio emission from stars encodes the conditions of the outer corona, mass-ejection events and space weather1,2,3,4,5. Previous low-frequency searches for radio-emitting stellar systems have lacked the sensitivity to detect the general population, instead largely focusing on targeted studies of anomalously active stars5,6,7,8,9. Here we present 19 detections of coherent radio emission associated with known M dwarfs from a blind flux-limited low-frequency survey. Our detections show that coherent radio emission is ubiquitous across the M dwarf main sequence, and that the radio luminosity is independent of known coronal and chromospheric activity indicators. While plasma emission can generate the low-frequency emission from the most chromospherically active stars of our sample1,10, the origin of the radio emission from the most quiescent sources is yet to be ascertained. Large-scale analogues of the magnetospheric processes seen in gas giant planets3,11,12 probably drive the radio emission associated with these quiescent stars. The slowest-rotating stars of this sample are candidate systems to search for star–planet interaction signatures.
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LOFAR visibilities taken before 2020 are publicly available via the LOFAR Long Term Archive (https://lta.lofar.eu/https://lta.lofar.eu/). The XMM-Newton data on LP 212-62, G 240-45, LP 169-22, and GJ 1151 are available through the XMM-Newton Science Archive (XSA; http://nxsa.esac.esa.int/nxsa-web). All other data used in the paper have been sourced from the public domain.
The important codes used to analyse the data are available at the following sites: WSClean (https://gitlab.com/aroffringa/wsclean) and DDF pipeline (https://github.com/mhardcastle/ddf-pipeline). This work has also made use of TOPCAT59, the IPYTHON package60; SciPy61; MATPLOTLIB, a PYTHON library for publication quality graphics62; ASTROPY, a community-developed core PYTHON package for astronomy63; and NUMPY64.
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The LOFAR data in this paper were (partly) processed by the LOFAR Two-Metre Sky Survey (LoTSS) team. This team made use of the LOFAR direction independent calibration pipeline (https://github.com/lofar-astron/prefactor), which was deployed by the LOFAR e-infragroup on the Dutch National Grid infrastructure with support of the SURF Co-operative through grant numbers e-infra 170194 e-infra 180169. The LoTSS direction-dependent calibration and imaging pipeline (http://github.com/mhardcastle/ddf-pipeline/) was run on compute clusters at Leiden Observatory and the University of Hertfordshire, which are supported by a European Research Council Advanced Grant (NEWCLUSTERS-321271) and the UK Science and Technology Funding Council (grant number ST/P000096/1). The Jülich LOFAR Long Term Archive and the German LOFAR network are both coordinated and operated by the Jülich Supercomputing Centre (JSC), and computing resources on the supercomputer JUWELS at JSC were provided by the Gauss Centre for Supercomputing e.V. (grant number CHTB00) through the John von Neumann Institute for Computing (NIC). 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. J.R.C. thanks the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) for support via the Talent Programme Veni grant. P.N.B. and J.S. are grateful for support from the UK STFC via grant number ST/R000972/1. R.J.v.W. acknowledges support from the Vidi research programme with project number 639.042.729, which is financed by the NWO. A.D. acknowledges support by the BMBF Verbundforschung under grant number 05A17STA. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and NASA’s Astrophysics Data System.
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Julien Morin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Callingham, J.R., Vedantham, H.K., Shimwell, T.W. et al. The population of M dwarfs observed at low radio frequencies. Nat Astron (2021). https://doi.org/10.1038/s41550-021-01483-0