Planet-induced radio emission from the coronae of M dwarfs: the case of Prox Cen and AU Mic

TL;DR

This study models stellar winds of Prox Cen and AU Mic to investigate star-planet interactions and the potential for radio emissions caused by electron cyclotron maser instability, revealing conditions under which such emissions could be detected.

Contribution

The paper introduces Alfvén wave-driven wind models incorporating magnetic field maps to assess star-planet radio interactions in M dwarfs, a novel approach for these systems.

Findings

Prox Cen's wind mass-loss rate is 0.25 solar masses per year.

AU Mic's wind mass-loss rate varies between 27 and 590 solar masses per year.

Planets around AU Mic could induce detectable radio emissions under certain wind conditions.

Abstract

There have recently been detections of radio emission from low-mass stars, some of which are indicative of star-planet interactions. Motivated by these exciting new results, in this paper we present Alfv\'en wave-driven stellar wind models of the two active planet-hosting M dwarfs Prox Cen and AU Mic. Our models incorporate large-scale photospheric magnetic field maps reconstructed using the Zeeman-Doppler Imaging method. We obtain a mass-loss rate of $0.25~\dot{M}_{\odot}$ for the wind of Prox Cen. For the young dwarf AU Mic, we explore two cases: a low and high mass-loss rate. Depending on the properties of the Alfv\'en waves which heat the corona in our wind models, we obtain mass-loss rates of $27$ and $590~\dot{M}_{\odot}$ for AU Mic. We use our stellar wind models to assess the generation of electron cyclotron maser instability emission in both systems, through a mechanism analogous to the sub-Alfv\'enic Jupiter-Io interaction. For Prox Cen we do not find any feasible scenario where the planet can induce radio emission in the star's corona, as the planet orbits too far from the star in the super-Alfv\'enic regime. However, in the case that AU Mic has a stellar wind mass-loss rate of $27~\dot{M}_{\odot}$, we find that both planets b and c in the system can induce radio emission from $\sim10$ MHz to 3 GHz in the corona of the host star for the majority of their orbits, with peak flux densities of $\sim10$ mJy. Detection of such radio emission would allow us to place an upper limit on the mass-loss rate of the star.