Abstract
AU Microscopii (AU Mic) is a young, active star whose transiting planet was recently detected. Here, we report our analysis of its TESS light curve, where we modeled the BY Draconis type quasi-periodic rotational modulation by starspots simultaneously to the flaring activity and planetary transits. We measured a flare occurrence rate in AU Mic of 6.35 flares per day for flares with amplitudes in the range of 0.06% < fmax < 1.5% of the star flux. We employed a Bayesian Markov chain Monte Carlo analysis to model the five transits of AU Mic b observed by TESS, improving the constraints on the planetary parameters. The measured planet-to-star effective radius ratio of Rp∕R⋆ = 0.0496 ± 0.0007 implies a physical radius of 4.07 ± 0.17 R⊕ and a planet density of 1.4 ± 0.4 g cm−3, confirming that AU Mic b is a Neptune-size moderately inflated planet. While a single feature possibly due to a second planet was previously reported in the former TESS data, we report the detection of two additional transit-like events in the new TESS observations of July 2020. This represents substantial evidence for a second planet (AU Mic c) in the system. We analyzed its three available transits and obtained an orbital period of 18.859019 ± 0.000016 d and a planetary radius of 3.24 ± 0.16 R⊕, which defines AU Mic c as a warm Neptune-size planet with an expected mass in the range of 2.2 M⊕ < Mc < 25.0 M⊕, estimated from the population of exoplanets of similar sizes. The two planets in the AU Mic system are in near 9:4 mean-motion resonance. We show that this configuration is dynamically stable and should produce transit-timing variations (TTV). Our non-detection of significant TTV in AU Mic b suggests an upper limit for the mass of AU Mic c of <7 M⊕, indicating that this planet is also likely to be inflated. As a young multi-planet system with at least two transiting planets, AU Mic becomes a key system for the study of atmospheres of infant planets and of planet-planet and planet-disk dynamics at the early stages of planetary evolution.
Highlights
Young planetary systems represent an opportunity to observe planets in the early stages of planetary formation when gravitational interactions have not significantly changed the initial configuration of the system
We present an analysis of the Transiting Exoplanet Survey Satellite (TESS) data of AU Microscopii (AU Mic), including the new observations obtained in July 2020, where we implement a multi-flare model combined with the starspots model, improving the constraints on the planetary parameters from transit modeling and allowing for the detection of two additional transits of the second candidate planet AU Mic c
We presented an analysis of the photometric TESS observations of the active young M1 star AU Mic, where we model the rotational modulation by starspots, the flaring activity, and the planetary transits simultaneously
Summary
Young planetary systems represent an opportunity to observe planets in the early stages of planetary formation when gravitational interactions have not significantly changed the initial configuration of the system. The AU Mic host is an M1 star with a spatially resolved edge-on debris disk (Kalas et al 2004) and at least one transiting planet, AU Mic b (Plavchan et al 2020). This Neptune-size planet is in a 8.5-d prograde orbit aligned with the stellar rotation axis (Martioli et al 2020; Hirano et al 2020; Palle et al 2020). While Plavchan et al (2020) only reported an upper limit on the mass of AU Mic b, Klein et al (2021) measured 17.1+−44..75 M⊕ thanks to infrared observations secured with the SPIRou spectropolarimeter (Donati et al 2020). Plavchan et al (2020) has reported the detection of an isolated transit event of a second possible candidate planet, hereafter referred to as AU Mic c
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
