New constraints on the planetary system around the young active star AU Mic. Two transiting warm Neptunes near mean-motion resonance

Abstract

AU Mic is a young, active star whose transiting planet was recently detected. We report our analysis of its TESS data, 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 of 6.35 flares per day for flares with amplitudes in the range of $0.06\%<f_{\max }<1.5\%$ of the star flux. We employed a Bayesian MCMC analysis to model the five transits of AU Mic b, improving the constraints on the planetary parameters. The planet radius of $4.07\pm 0.17$~R${}_{\oplus }$ and a mean density of $1.4\pm 0.4$~g~cm${}^{-3}$ confirms that it 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 transits and obtained an orbital period of $18.859019\pm 0.000016$~d and a planetary radius of $3.24\pm 0.16$~R${}_{\oplus }$, which defines it as a warm Neptune-size planet with an expected mass in the range of 2.2~M${}_{\oplus }$~$<M_{\mathrm{c}}<$25.0~M${}_{\oplus }$. The two planets in the 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${}_{\oplus }$, 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.

Accepted for publication in Section 10. Planets and planetary systems of A&A

References in corpus (10)

• The Transiting Exoplanet Survey Satellite
• Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass
• On the age of the $\beta$ Pictoris moving group
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• A planet within the debris disk around the pre-main-sequence star AU Microscopii
• SPIRou: nIR velocimetry & spectropolarimetry at the CFHT
• The HARPS search for southern extra-solar planets XIX. Characterization and dynamics of the GJ876 planetary system
• Investigating the young AU~Mic system with SPIRou: large-scale stellar magnetic field and close-in planet mass
• Limits on the Spin-Orbit Angle and Atmospheric Escape for the 22 Myr-old Planet AU Mic b
• Spin-orbit alignment and magnetic activity in the young planetary system AU Mic

Cited by in corpus (61)

• The 10 parsec sample in the Gaia era
• Planet-induced radio emission from the coronae of M dwarfs: the case of Prox Cen and AU Mic
• TESS Hunt for Young and Maturing Exoplanets (THYME) VI: an 11 Myr giant planet transiting a very low-mass star in Lower Centaurus Crux
• The magnetic field and multiple planets of the young dwarf AU~Mic
• Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System
• One year of AU Mic with HARPS: II -- stellar activity and star-planet interaction
• Flares, Rotation, and Planets of the AU Mic System from TESS Observations
• Planet populations inferred from debris discs: insights from 178 debris systems in the ISPY, LEECH and LIStEN planet-hunting surveys
• One year of AU Mic with HARPS: I -- measuring the masses of the two transiting planets
• Hubble Space Telescope transmission spectroscopy for the temperate sub-Neptune TOI-270d: a possible hydrogen-rich atmosphere containing water vapour
• PySME -- Spectroscopy Made Easier
• The young HD 73583 (TOI-560) planetary system: Two 10-M${}_{\oplus }$ mini-Neptunes transiting a 500-Myr-old, bright, and active K dwarf
• Constraints on the mass and atmospheric composition and evolution of the low-density young planet DS Tuc A b
• The GAPS Programme with HARPS-N at TNG. XXXVII. A precise density measurement of the young ultra-short period planet TOI-1807 b
• The CARMENES search for exoplanets around M dwarfs. Mapping stellar activity indicators across the M dwarf domain
• AU Microscopii in the FUV: Observations in Quiescence, During Flares, and Implications for AU Mic b and c
• Simulating the Space Weather in the AU Mic System: Stellar Winds and Extreme Coronal Mass Ejections
• Constraining atmospheric parameters and surface magnetic fields with $\text{ZeeTurbo}$: an application to SPIRou spectra
• Homogeneous search for helium in the atmosphere of 11 gas giant exoplanets with SPIRou
• A Seven-Day Multi-Wavelength Flare Campaign on AU Mic I: High-Time Resolution Light Curves and the Thermal Empirical Neupert Effect
• TOI-1759 b: a transiting sub-Neptune around a low mass star characterized with SPIRou and TESS
• New Coronae and Stellar Associations Revealed by a Clustering Analysis of the Solar Neighborhood
• Searching for flaring star-planet interactions in AU Mic TESS observations
• Monitoring the young planet host V1298 Tau with SPIRou: planetary system and evolving large-scale magnetic field
• Revisiting K2-233 spectroscopic time-series with multidimensional Gaussian Processes
• TESS Investigation -- Demographics of Young Exoplanets (TI-DYE) II: a second giant planet in the 17-Myr system HIP 67522
• A 38 Million Year Old Neptune-Sized Planet in the Kepler Field
• Transit timing variations of AU Microscopii b and c
• Space Weather-driven Variations in Ly$\alpha$ Absorption Signatures of Exoplanet Atmospheric Escape: MHD Simulations and the Case of AU Mic b
• Radial Velocity Survey for Planets around Young stars (RVSPY) A transiting warm super-Jovian planet around HD 114082, a young star with a debris disk
• Probing atmospheric escape through metastable He I triplet lines in 15 exoplanets observed with SPIRou
• TOI-1268b: the youngest, hot, Saturn-mass transiting exoplanet
• Short term variability of DS Tuc A observed with TESS
• Planetary parameters, XUV environments and mass-loss rates for nearby gaseous planets with X-ray detected host-stars
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) I: Motivation, sample, data reduction, and results overview
• Rave: A non-parametric method for recovering the surface brightness and height profiles of edge-on debris disks
• Multiwavelength Vertical Structure in the AU Mic Debris Disk: Characterizing the Collisional Cascade
• The Variable Detection of Atmospheric Escape around the young, Hot Neptune AU Mic b
• The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc
• A possible misaligned orbit for the young planet AU Mic c
• TOI-837b is a Young Saturn-sized Exoplanet with a Massive 70 $M_{\oplus }$ Core
• Can comets deliver prebiotic molecules to rocky exoplanets?
• TOI-1736 and TOI-2141: two systems including sub-Neptunes around solar analogs revealed by TESS and SOPHIE
• Flybys in debris disk systems with Gaia eDR3
• Stellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU~Microscopii
• Probing the innermost region of the AU~Microscopii debris disk
• TOI-837 b: characterisation, formation and evolutionary history of an infant warm Saturn-mass planet
• The strong suppression of Galactic cosmic rays reaching AU Mic b, c and Prox Cen b
• Spectroscopic observations of flares and superflares on AU Mic
• Characterization of debris disks observed with SPHERE
• NIGHT: a compact, near-infrared, high-resolution spectrograph to survey helium in exoplanet systems
• Solar and stellar flares: frequency, active regions and stellar dynamo
• The Mysterious Affair of the H${}_2$ in AU Mic
• A Seven-Day Multi-Wavelength Flare Campaign on AU Mic III: Quiescent and Flaring Properties of the X-ray Spectra and Chromospheric lines
• Multi-wavelength aperture polarimetry of debris disc host stars
• TOI-3568 b: a super-Neptune in the sub-Jovian desert
• The CARMENES search for exoplanets around M dwarfs : Understanding the wavelength dependence of radial velocity measurements
• Far-ultraviolet flares and variability of the young M dwarf AU Mic: a non-detection of planet c in transit at Lyman-alpha
• Nearby Young Stars and Young Moving Groups
• The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and Transit Timing Variations as seen by CHEOPS and TESS
• Scientific Validation of the SPARC4 Pipeline: Multi-band Imaging, Polarimetry, and Photometric Time Series for Improved Characterization of Transiting Exoplanets