Radio Emission from Red-Giant Hot Jupiters

TL;DR

Red-Giant Hot Jupiters, planets around evolved stars, could emit detectable radio waves due to stellar wind interactions, potentially observable with future low-frequency radio telescopes like the SKA.

Contribution

This paper estimates the radio emission from Red-Giant Hot Jupiters and assesses their detectability with upcoming radio observatories.

Findings

RGHJs may be as bright or brighter than hot Jupiters around main-sequence stars.

Radio signals from RGHJs could be detectable up to a few hundred parsecs.

Detection is feasible with the Square Kilometer Array.

Abstract

When planet-hosting stars evolve off the main sequence and go through the red-giant branch, the stars become orders of magnitudes more luminous and, at the same time, lose mass at much higher rates than their main-sequence counterparts. Accordingly, if planetary companions exist around these stars at orbital distances of a few AU, they will be heated up to the level of canonical hot Jupiters and also be subjected to a dense stellar wind. Given that magnetized planets interacting with stellar winds emit radio waves, such "Red-Giant Hot Jupiters" (RGHJs) may also be candidate radio emitters. We estimate the spectral auroral radio intensity of RGHJs based on the empirical relation with the stellar wind as well as a proposed scaling for planetary magnetic fields. RGHJs might be intrinsically as bright as or brighter than canonical hot Jupiters and about 100 times brighter than equivalent objects around main-sequence stars. We examine the capabilities of low-frequency radio observatories to detect this emission and find that the signal from an RGHJ may be detectable at distances up to a few hundred parsecs with the Square Kilometer Array.