INTRODUCTORY PARAGRAPHCoherent low-frequency ( 200 MHz) radio emission from stars encodes the conditions of the outer corona, mass-ejection events, and space weather 1,2,3,4,5 . 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 stars 2,6,7,8,9 . 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 sample 1,10 , 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 planets 4,11,12 likely 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.

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 are specified, namely the plasma density in the outer corona and the radial distance at which the plasma forces the closed magnetic field into an open geometry. Low frequency radio observations (ν 200 MHz) of plasma and cyclotron emission from stars probe these magneto-ionic conditions. Here we report the detection of low-frequency (120 − 167 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 region extends to at least ≈ 10 stellar radii, which is about a factor of a few larger than the solar value, and possibly to 20 stellar radii. Our results suggest that the magnetic-field structure of M dwarfs is in between Sunlike and planet-like configurations, where compact over-dense coronal loops with X-ray emitting plasma co-exist with a large-scale magnetosphere with a lower plasma density and closed magnetic geometry.

We observed the flare stars AD Leonis, Wolf 424, EQ Pegasi, EV Lacertae, and UV Ceti for nearly 135 hours. These stars were observed between 63 and 83 MHz using the interferometry mode of the Long Wavelength Array. Given that emission from flare stars is typically circularly polarized, we used the condition that any significant detection present in Stokes I must also be present in Stokes V at the same time in order for us to consider it a possible flare. Following this, we made one marginal flare detection for the star EQ Pegasi. This flare had a flux density of 5.91 Jy in Stokes I and 5.13 Jy in Stokes V, corresponding to a brightness temperature 1.75 × 10 16 (r/r * ) −2 K.