Searching for planet-induced radio signals from the young close-in planet host star HIP 67522

¹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, Dwingeloo 7991 PD, The Netherlands
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
³ Anton Pannenkoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

^★ Corresponding author: ilin@astron.nl

Received: 21 March 2025
Accepted: 3 June 2025

Abstract

HIP 67522 is a 17 Myr old 1.2 M_⊙ dwarf. It is the only such young star known to host two close-in gas giant planets. The inner planet likely orbits close enough to its host to power magnetic star-planet interactions. In the radio domain, magnetic star-planet interaction is expected to produce a unique signature: electron cyclotron maser emission (ECME), beamed in phase with the orbit of the close-in planet. We conducted the longest radio monitoring campaign of a G dwarf host star to date to search for ECME, totaling 135 h on HIP 67522 over a period of five months with the Australia Telescope Compact Array (ATCA) between 1.1 – 3.1 GHz. We find that HIP 67522 is active in the radio, with emission that varies stochastically, with a duty cycle of 69% above 0.24 mJy, and frequent bursts. Both the bursts and the quiescent emission are consistent with the canonical Güdel-Benz relation, and show a positive spectral index and brightness temperatures ≥ 10¹⁰ K, indicating likely a flaring origin. Our observations cover 61% of the innermost planet’s orbit, including multiple visits of the quadrature where planet-induced ECME detection is most likely for this system. However, no orbital modulation or persistent polarization of the radio emission was detected. Our upper limit on circularly polarized emission from HIP 67522 suggests a <0.7% conversion efficiency of the magnetic power generated in the star-planet interaction into radio waves, unless the emission was missed by our phase or frequency coverage, or was absorbed in the circumstellar plasma. HIP 67522 is a system with one of the highest expected powers of star-planet interaction among known systems and shows strong indication of planet-induced flaring, motivating observations at other wavelengths to probe for additional dissipation pathways.