Searching for flaring star-planet interactions in AU Mic TESS observations

TL;DR

This study investigates magnetic star-planet interactions in AU Mic using TESS optical data, finding hints of possible SPI signals in flare distributions that could be confirmed with extended observations.

Contribution

It introduces a customized statistical method to detect star-planet magnetic interactions in optical light curves, focusing on AU Mic and its planet AU Mic b.

Findings

No definitive SPI detection in 50 days of data

Strongest deviation observed at the planet's orbital period

Extended observations could confirm SPI with >3σ significance

Abstract

Planets that closely orbit magnetically active stars are thought to be able to interact with their magnetic fields in a way that modulates stellar activity. This modulation in phase with the planetary orbit, such as enhanced X-ray activity, chromospheric spots, radio emission, or flares, is considered the clearest sign of magnetic star-planet interaction (SPI). However, the magnitude of this interaction is poorly constrained, and the intermittent nature of the interaction is a challenge for observers. AU Mic is an early M dwarf, and the most actively flaring planet host detected to date. Its innermost companion, AU Mic b, is a promising target for magnetic SPI observations. We used optical light curves of AU Mic obtained by the Transiting Exoplanet Survey Satellite to search for signs of flaring SPI with AU Mic b using a customized Anderson-Darling test. In the about $50$ days of observations, the flare distributions with orbital, rotational, and synodic periods were generally consistent with intrinsic stellar flaring. We found the strongest deviation ($p=0.07,\;n=71$) from intrinsic flaring with the orbital period of AU Mic b, in the high energy half of our sample ($ED>1$ s). If it reflects the true SPI signal from AU Mic b, extending the observing time by a factor of $2-3$ will yield a $>3\sigma$ detection. Continued monitoring of AU Mic may therefore reveal flaring SPI with orbital phase, while rotational modulation will smear out due to the star's strong differential rotation.