Radio Emission from UV Cet: Auroral Emission from a Stellar Magnetosphere

TL;DR

This study reports detailed radio observations of UV Cet, revealing auroral emissions likely caused by cyclotron maser instability, with polarization characteristics suggesting complex magnetic and plasma interactions in the stellar magnetosphere.

Contribution

First detailed dynamic spectra of UV Cet's radio emission at high resolution, with a model explaining polarization features through magnetic field and plasma density considerations.

Findings

Detected broadband arcs with high circular polarization

Observed elliptically polarized bursts indicating complex plasma interactions

Proposed a model linking emission features to stellar magnetic field and plasma structures

Abstract

The archetypical flare star UV Cet was observed by MeerKAT on 5-6 October 2021. A large radio outburst with a duration of $\sim\!2$ hr was observed between 886-1682 MHz with a time resolution of 8s and a frequency resolution of 0.84 MHz, enabling sensitive dynamic spectra to be formed. The emission is characterized by three peaks containing a multitude of broadband arcs or partial arcs in the time-frequency domain. In general, the arcs are highly right-hand circularly polarized. During end of the third peak, brief bursts occur that are significantly elliptically polarized. We present a simple model that appears to be broadly consistent with the characteristics of the radio emission from UV Cet. Briefly, the stellar magnetic field is modeled as a dipole aligned with the rotational axis of the star. The radio emission mechanism is assumed to be due to the cyclotron maser instability where x-mode radiation near the electron gyrofrequency is amplified. While the elliptically polarized bursts may be intrinsic to the source, rather stringent limits are imposed on the plasma density in the source and along the propagation path. We suggest that the elliptically polarized radiation may instead be the result of reflection on an over-dense plasma structure at some distance from the source. Radio emission from UV~Cet shares both stellar and planetary attributes.