TOI-3884 b: A rare 6-R${}_{\oplus }$ planet that transits a low-mass star with a giant and likely polar spot

Abstract

The Transiting Exoplanet Survey Satellite mission identified a deep and asymmetric transit-like signal with a periodicity of 4.5 days orbiting the M4 dwarf star TOI-3884. The signal has been confirmed by follow-up observations collected by the ExTrA facility and Las Cumbres Observatory Global Telescope, which reveal that the transit is chromatic. The light curves are well modelled by a host star having a large polar spot transited by a 6-R${}_{\oplus }$ planet. We validate the planet with seeing-limited photometry, high-resolution imaging, and radial velocities. TOI-3884 b, with a radius of $6.00\pm 0.18$ R${}_{\oplus }$, is the first sub-Saturn planet transiting a mid-M dwarf. Owing to the host star's brightness and small size, it has one of the largest transmission spectroscopy metrics for this planet size and becomes a top target for atmospheric characterisation with the James Webb Space Telescope and ground-based telescopes.

13 pages, 13 figures, accepted for publication in A&A Letters

References in corpus (28)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• The Transiting Exoplanet Survey Satellite
• The James Webb Space Telescope
• Gaia Early Data Release 3: The astrometric solution
• Gaia Early Data Release 3: Photometric content and validation
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission
• ESPRESSO@VLT -- On-sky performance and first results
• Large-scale magnetic topologies of early M dwarfs
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• The large-scale axisymmetric magnetic topology of avery-low-mass fully-convective star
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
• Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK
• SPIRou: nIR velocimetry & spectropolarimetry at the CFHT
• A giant exoplanet orbiting a very low-mass star challenges planet formation models
• Planetary system LHS 1140 revisited with ESPRESSO and TESS
• SPIRou Input Catalog: Activity, Rotation and Magnetic Field of Cool Dwarfs
• The Rossiter-McLaughlin effect Revolutions: An ultra-short period planet and a warm mini-Neptune on perpendicular orbits
• The TESS Faint Star Search: 1,617 TOIs from the TESS Primary Mission
• Mapping stellar surfaces I: Degeneracies in the rotational light curve problem
• Gaia Search for stellar Companions of TESS Objects of Interest
• Mapping stellar surfaces II: An interpretable Gaussian process model for light curves
• Gaia Search for stellar Companions of TESS Objects of Interest II
• Efficient and precise transit light curves for rapidly-rotating, oblate stars

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• A low-mass sub-Neptune planet transiting the bright active star HD 73344
• The changing transit shape of TOI-3884 b
• Homogeneous search for spot transits in Kepler and TESS photometry of K $-$ M-type main-sequence stars
• A Panchromatic JWST Spectrum of a Giant Starspot on the Fully Convective M-dwarf TOI-3884
• A sub-Saturn Mass-Radius Desert for Planets with Equilibrium Temperature Less than 600 K