Polarized, variable radio emission from the scallop-shell binary system DG CVn

¹ Institut de Ciències de I’Espai (ICE-CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Cerdanyola del Vallès, Catalonia, Spain
² Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels, Barcelona, Catalonia, Spain
³ Institute of Applied Computing & Community Code (IAC3), University of the Balearic Islands, Palma, 07122 Spain
⁴ Department of Physics & Astronomy, Bucknell University, Lewisburg, PA, USA
⁵ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁷ Centre for Planetary Habitability, Department of Geosciences, University of Oslo, Sem Saelands vei 2b, 0315 Oslo, Norway
⁸ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁹ Observatories of the Carnegie Institution for Science, Pasadena, CA, 91101 USA
¹⁰ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, Dwingeloo, 7991 PD The Netherlands
¹¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, E-18008 Granada, Spain
¹² Center for Astroparticles and High Energy Physics (CAPA), Universidad de Zaragoza, E-50009 Zaragoza, Spain
¹³ School of Sciences, European University Cyprus, Diogenes street, Engomi, 1516 Nicosia, Cyprus

^⋆ Corresponding author: kaur@ice.csic.es

Received: 19 April 2025
Accepted: 11 July 2025

Abstract

DG CVn is an eruptive variable star and represents the closest member of the known sample of complex periodic variables, or scallop-shell stars. Over the years, this M dwarf binary system has shown significant flaring activity at a wide range of frequencies. Here, we present a detailed analysis of ∼14 hours of radio observations of this stellar system, taken with the Karl G. Jansky Very Large Array at band L, centered at 1.5 GHz. In both 7-hour-long observations we have found a quiescent, weakly polarized component that could be ascribable to the incoherent, gyro-synchrotron emission coming from the magnetosphere surrounding one or both stars, along with multiple ∼90% right-circularly polarized bursts, some of which last for a few minutes and others of which last longer, ≳30 minutes Some of these bursts show a drift in frequency and time, possibly caused due to beaming effects or the motion of the plasma responsible for the emission. We assess the possible modulation of burst frequency with the primary and secondary periods, and discuss the properties of these bursts, favoring electron cyclotron maser over plasma emission as the likely underlying mechanism. We compare DG CVn’s dynamic spectrum to other young M dwarfs and find many similarities. A proper, dedicated, simultaneous radio/optical follow-up is needed to monitor the long-term variability and increase the statistics of bursts, in order to test whether the corotating absorbers detected in the optical can drive the observed radio emission, and whether the occurrence of radio bursts correlates with the rotational phase of either star.