Radio emission from flaring stars and brown dwarfs

¹ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
² CSFK, MTA Centre of Excellence, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary

^★ Corresponding author: perger.krisztina@csfk.org

Received: 4 April 2025
Accepted: 24 June 2025

Abstract

Context. The vicinities of intermediate-to-late type dwarf stars are considered as an adequate terrain to host planets suitable for life to form. However, they oftentimes show increased stellar activity, which should be taken into consideration when seeking potential habitable planetary systems.

Aims. With the aim to reveal the effects of the magnetic field to the multi-band activity of dwarf stars, we search for associated radio emission for an extensive list of 14 915 brown dwarfs and 15 124 flaring stars.

Methods. We utilised the first and second epoch catalogues and radio maps from all three epochs of the VLASS, supplemented with X-ray catalogues based on observations by the ROSAT, eROSITA, and XMM-Newton space telescopes, and 2-minute cadence optical light curves from the TESS mission. The radio-detected sub-sample was queried for concurrent TESS observations, and sources with coinciding light-curves were studied individually.

Results. We found no associated radio emission for brown dwarfs, and found 55 radio counterparts for the sample of flaring stars, out of which seven have coincident TESS observations. The radio-detected sample follows both the radio-X-ray and the period-activity relations. We found a strong correlation between the radio powers and the stellar parameters of surface gravity, radius, and mass. We found no connection between the flare rate and the radio variability. For radio-detected stars with available effective temperatures and rotational periods, we estimated gyrochronological ages, which resulted in values of T_gyro ≲ 1 Gyr, with the majority of the sample being younger than 150 Myr. We found no strong connection between the occurrence of optical flares and radio variability for the individually studied stars.

Conclusions. We conclude that radio emission from intermediate-to-late type flaring stars is of synchrotron nature, and shares a common origin with X-ray processes. It is created by a predominantly young stellar population, and is the collective contribution of stellar flares, accretion, and coronal heating.