A Radio Search for Star-Planet Interaction in TOI-540 and SPECULOOS-3

TL;DR

This study conducted deep radio observations of two exoplanet systems, TOI-540 and SPECULOOS-3, to detect star-planet magnetic interactions, but found no evidence of such emissions within their sensitivity limits.

Contribution

First targeted centimeter-band radio observations of these exoplanet systems aimed at detecting star-planet magnetic interactions, providing constraints on planetary magnetic fields.

Findings

No radio emission detected from either system.

Observations sensitive enough to detect SPI if present with planetary magnetic fields as low as 1 G.

Constraints on planetary magnetic field strengths based on non-detections.

Abstract

We present the first targeted centimeter-band radio observations of two recently-discovered exoplanet systems that are prime candidates for magnetic star-planet interaction (SPI): TOI-540 and SPECULOOS-3. The targets were selected due to the small orbital separation of their known planets, as well as for indications of stellar magnetic activity, given that for SPI radio emission may be strongest when a sufficiently magnetized star hosts a close-in planet. The deep, multi-epoch Very Large Array (SPECULOOS-3) and MeerKAT (TOI-540) observations yield non-detections, with $3\sigma$ limits of $\lesssim 7.5$ $\mu$Jy ($4-8$ GHz) and $\lesssim 30-80$ $\mu$Jy ($0.8-1.7$ GHz), respectively. For SPECULOOS-3 b we rule out observable SPI for most of its orbit, while for TOI-540 b we sample a narrower range, around planetary transit. We model possible planetary magnetic field strength constraints for both systems, and conclude that our observations are sensitive enough to sample SPI emission in these systems if present and directed at us, even for a planetary field of only $\sim 1$ G.