Star-Planet Interaction at radio wavelengths in YZ Ceti: Inferring planetary magnetic field

TL;DR

This study reports the first confirmed detection of star-planet interaction at radio wavelengths in the YZ Ceti system, revealing insights into the magnetic fields of both star and planet through auroral radio emissions.

Contribution

The paper presents observational evidence of star-planet interaction via radio emissions, estimating magnetic field strengths for the star and planet, and demonstrating the potential of radio observations to study exoplanet magnetic environments.

Findings

Detected radio emissions consistent with star-planet interaction

Estimated stellar magnetic field of about 2.4 kG

Lower limit for planetary magnetic field of 0.4 G

Abstract

In exoplanetary systems, the interaction between the central star and the planet can trigger Auroral Radio Emission (ARE), due to the Electron Cyclotron Maser mechanism. The high brightness temperature of this emission makes it visible at large distances, opening new opportunities to study exoplanets and to search for favourable conditions for the development of extra-terrestrial life, as magnetic fields act as a shield that protects life against external particles and influences the evolution of the planetary atmospheres. In the last few years, we started an observational campaign to observe a sample of nearby M-type stars known to host exoplanets with the aim to detect ARE. We observed YZ Ceti with the upgraded Giant Metrewave Radio Telescope (uGMRT) in band 4 (550-900 MHz) nine times over a period of five months. We detected radio emission four times, two of which with high degree of circular polarization. With statistical considerations we exclude the possibility of flares due to stellar magnetic activity. Instead, when folding the detections to the orbital phase of the closest planet YZ Cet b, they are at positions where we would expect ARE due to star-planet interaction (SPI) in sub-Alfvenic regime. With a degree of confidence higher than 4.37 sigma, YZ Cet is the first extrasolar systems with confirmed SPI at radio wavelengths. Modelling the ARE, we estimate a magnetic field for the star of about 2.4 kG and we find that the planet must have a magnetosphere. The lower limit for the polar magnetic field of the planet is 0.4 G.