Magnetic interactions between the newfound planet, designated Gliese 1151b, and its host star are the likely source of low-frequency radio emission recently detected from this system.
This is an artistic impression of a red dwarf star’s magnetic interaction with its exoplanet. Image credit: Danielle Futselaar, Artsource.nl.
“Planets in close-in orbits are embedded in a magnetized stellar wind from the expanding stellar corona,” Professor Suvrath Mahadevan from the Department of Astronomy & Astrophysics at the Pennsylvania State University and colleagues wrote in their paper.
“As they orbit, short-period planets can perturb the flow of the magnetized wind, which can carry substantial amounts of energy towards the host star via sub-Alfvénic interactions.”
“This incoming energy can heat up the chromosphere of the star, causing a hot spot on the surface of the star, which can cause variability that is modulated by the orbital period of the planet.”
In 2019, a team of astronomers from Europe and the United States discovered highly circularly polarized radio emission at 150 MHz in the direction of Gliese 1151, a quiescent M4.5 dwarf star located 26 light-years away in the constellation of Ursa Major, using the LOFAR Telescope Array.
The emission properties were consistent with theoretical expectations for star-planet interaction with a rocky planet in an approximately one- to five-day-long orbit.
Professor Mahadevan and co-authors aimed to detect the candidate planet using a radial-velocity method.
They analyzed data collected by the Habitable-zone Planet Finder (HPF) spectrometer on the 10-m Hobby-Eberly Telescope at McDonald Observatory, the HARPS-N spectrograph at Telescopio Nazionale Galileo, and NASA’s Transiting Exoplanet Survey Satellite (TESS).
The observation revealed a periodic Doppler signature consistent with an exoplanet on a 2.02-day orbit.
“From radial velocities obtained with HPF and HARPS-N, we constrain the planet minimum mass to be 2.5 Earth masses,” the astronomers wrote.
“This detection encourages further synergies of precision radial velocity and low-frequency radio observations with facilities such as LOFAR and the Square Kilometre Array in the future to detect and characterize planets around nearby stars exhibiting coherent radio emission.”
Suvrath Mahadevan et al. 2021. The Habitable-zone Planet Finder Detects a Terrestrial-mass Planet Candidate Closely Orbiting Gliese 1151: The Likely Source of Coherent Low-frequency Radio Emission from an Inactive Star. ApJL, in press; arXiv: 2102.02233