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

Abstract

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 Alfvén 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 $0.25~\dot{\mathrm{ M}}_{\odot }$ for the wind of Prox Cen. For the young dwarf AU Mic, we explore two cases: a low and a high mass-loss rate. Depending on the properties of the Alfvén waves that heat the corona in our wind models, we obtain mass-loss rates of 27 and $590~\dot{\mathrm{ M}}_{\odot }$ 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-Alfvénic 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-Alfvénic regime. However, in the case that AU Mic has a stellar wind mass-loss rate of $27~\dot{\mathrm{ M}}_{\odot }$, we find that both planets b and c in the system can induce radio emission from ∼10 MHz to 3 GHz in the corona of the host star for the majority of their orbits, with peak flux densities of ∼10 mJy. Detection of such radio emission would allow us to place an upper limit on the mass-loss rate of the star.