A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776

Abstract

We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776, J = 8.5 mag, M = 0.54+-0.03 Msun) detected during Sector 10 observations of the Transiting Exoplanet Survey Satellite (TESS). Combining the TESS photometry with HARPS radial velocities, as well as ground-based follow-up transit observations from MEarth and LCOGT telescopes, we measured for the inner planet, TOI-776 b, a period of 8.25 d, a radius of 1.85+-0.13 Re, and a mass of 4.0+-0.9 Me; and for the outer planet, TOI-776 c, a period of 15.66 d, a radius of 2.02+-0.14 Re, and a mass of 5.3+-1.8 Me. The Doppler data shows one additional signal, with a period of 34 d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776 b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54 Msun. Due to the brightness of the star, the TOI-776 system is also an excellent target for the James Webb Space Telescope, providing a remarkable laboratory to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.

arXiv comment26 pages, 15 figures, 8 tables. Accepted for publication in Astronomy & Astrophysics

References in corpus (133)

• Gaia Data Release 2. Summary of the contents and survey properties
• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Bayes in the sky: Bayesian inference and model selection in cosmology
• The WASP Project and the SuperWASP Cameras
• Las Cumbres Observatory Global Telescope Network
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)
• REBOUND: An open-source multi-purpose N-body code for collisional dynamics
• batman: BAsic Transit Model cAlculatioN in Python
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• Elemental Abundance Survey of The Galactic Thick Disk
• Mass-Radius Relationships for Solid Exoplanets
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Kepler planets: a tale of evaporation
• Atmospheric Escape from Hot Jupiters
• IAS15: A fast, adaptive, high-order integrator for gravitational dynamics, accurate to machine precision over a billion orbits
• The TESS Input Catalog and Candidate Target List
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves (Expanded Edition)
• The Occurrence Rate of Small Planets around Small Stars
• Milky Way Cepheid Standards for Measuring Cosmic Distances and Application to Gaia DR2: Implications for the Hubble Constant
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• Growth Model Interpretation of Planet Size Distribution
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• Northern Sky Variability Survey (NSVS): Public data release
• RadVel: The Radial Velocity Modeling Toolkit
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• Core-powered mass loss and the radius distribution of small exoplanets
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• The Catalina Surveys Periodic Variable Star Catalog
• Planetary evaporation by UV & X-ray radiation: basic hydrodynamics
• Mass-Radius Relation for Rocky Planets based on PREM
• Sculpting the Valley in the Radius Distribution of Small Exoplanets as a by-product of Planet Formation: The Core-Powered Mass-Loss Mechanism
• Estimation of the XUV radiation onto close planets and their evaporation
• The MUSCLES Treasury Survey I: Motivation and Overview
• Characterizing transiting exoplanet atmospheres with JWST
• The HARPS-TERRA project I. Description of the algorithms, performance and new measurements on a few remarkable stars observed by HARPS
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• Juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems
• Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes
• PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST
• Kepler Data Validation I -- Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates
• A new list of thorium and argon spectral lines in the visible
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
• Eccentricity from transit photometry: small planets in Kepler multi-planet systems have low eccentricities
• On the use of Gaia magnitudes and new tables of bolometric corrections
• Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
• Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
• Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Limb darkening and exoplanets: testing stellar model atmospheres and identifying biases in transit parameters
• Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1
• The orbital eccentricity of small planet systems
• The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star
• A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses
• Kepler Data Validation II -- Transit Model Fitting and Multiple-Planet Search
• Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b
• Exoplanet Orbital Eccentricities Derived From LAMOST-Kepler Analysis
• SOAR TESS Survey. I: Sculpting of TESS planetary systems by stellar companions
• Evolutionary Analysis of Gaseous Sub-Neptune-Mass Planets with MESA
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• Kepler Planet Masses and Eccentricities from TTV Analysis
• Ranges of Atmospheric Mass and Composition of Super Earth Exoplanets
• HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance
• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• Signatures of the Core-Powered Mass-Loss Mechanism in the Exoplanet Population: Dependence on Stellar Properties and Observational Predictions
• The CARMENES search for exoplanets around M dwarfs: Different roads to radii and masses of the target stars
• Ten years of speckle interferometry at SOAR
• Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
• Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• A new equation of state for dense hydrogen-helium mixtures
• Transit Detection in the MEarth Survey of Nearby M Dwarfs: Bridging the Clean-First, Search-Later Divide
• The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
• Confirmation of the $Gaia$ DR2 parallax zero-point offset using asteroseismology and spectroscopy in the $Kepler$ field
• Evolution of the radius valley around low mass stars from $Kepler$ and $K2$
• CARMENES input catalogue of M dwarfs V. Luminosities, colours, and spectral energy distributions
• A nearby M star with three transiting super-Earths discovered by K2
• How formation time-scales affect the period dependence of the transition between rocky super-Earths and gaseous sub-Neptunes and implications for ${\eta }_{\oplus }$
• Secure TTV Mass Measurements: Ten Kepler Exoplanets between 3 and 8 Earth Masses with Diverse Densities and Incident Fluxes
• Flares from small to large: X-ray spectroscopy of Proxima Centauri with XMM-Newton
• The M dwarf planet search programme at the ESO VLT + UVES. A search for terrestrial planets in the habitable zone of M dwarfs
• Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization
• The interior and atmosphere of the habitable-zone exoplanet K2-18b
• Planetary evolution with atmospheric photoevaporation I. Analytical derivation and numerical study of the evaporation valley and transition from super-Earths to sub-Neptunes
• Mass and Mass Scalings of Super-Earths
• A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap
• A Definition for Giant Planets Based on the Mass-Density Relationship
• CARMENES input catalogue of M dwarfs IV. New rotation periods from photometric time series
• Scaling K2. I. Revised Parameters for 222,088 K2 Stars and a K2 Planet Radius Valley at 1.9 $R_{\oplus }$
• Mass-Radius Relations and Core-Envelope Decompositions of Super-Earths and Sub-Neptunes
• A super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266
• Pyaneti: a fast and powerful software suite for multi-planet radial velocity and transit fitting
• The Monitor project: Data processing and lightcurve production
• Exoplanets around Low-mass Stars Unveiled by K2
• Planetary system LHS 1140 revisited with ESPRESSO and TESS
• Absence of a metallicity effect for ultra-short-period planets
• The CARMENES search for exoplanets around M dwarfs. Two planets on the opposite sides of the radius gap transiting the nearby M dwarf LTT 3780
• Testing exoplanet evaporation with multi-transiting systems
• Characterization of the L 98-59 multi-planetary system with HARPS: two confirmed terrestrial planets and a mass upper limit on the third
• Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths"
• XUV exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets II: Hydrogen coronae and ion escape
• Quantifying the Bayesian Evidence for a Planet in Radial Velocity Data
• Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits
• Three Small Super-Earths Transiting the nearby star GJ 9827
• From cold to hot irradiated gaseous exoplanets: Fingerprints of chemical disequilibrium in atmospheric spectra
• Precise mass and radius of a transiting super-Earth planet orbiting the M dwarf TOI-1235: a planet in the radius gap?
• TOI-1235 b: a keystone super-Earth for testing radius valley emergence models around early M dwarfs
• From cold to hot irradiated gaseous exoplanets: Toward an observation-based classification scheme
• In hot water: effects of temperature-dependent interiors on the radii of water-rich super-Earths
• Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS
• A HARPS view on K2-3
• Absolute densities in exoplanetary systems: photodynamical modelling of Kepler-138
• K2-146: Discovery of Planet c, Precise Masses from Transit Timing, and Observed Precession
• The role of clouds on the depletion of methane and water dominance in the transmission spectra of irradiated exoplanets
• Know thy star, know thy planet: Chemo-kinematically characterizing TESS targets
• The Effects of Stellar Companions on Exoplanet Radius Distributions
• Theoretical Reflectance Spectra of Earth-Like Planets through Their Evolutions: Impact of Clouds on the Detectability of Oxygen, Water, and Methane with Future Direct Imaging Missions
• K2-110 b - a massive mini-Neptune exoplanet
• Cycle period, differential rotation and meridional flow for early M dwarf stars
• It takes two planets in resonance to tango around K2-146
• The existence of the Lambda effect in the solar convection zone indicated by SDO observations
• Two planetary systems with transiting Earth-size and super-Earth planets orbiting late-type dwarf stars

Cited by in corpus (34)

• Habitability and Biosignatures of Hycean Worlds
• The Hazy and Metal-Rich Atmosphere of GJ 1214 b Constrained by Near and Mid-Infrared Transmission Spectroscopy
• ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations
• How Deep Is the Ocean? Exploring the phase structure of water-rich sub-Neptunes
• TOI-1452 b: SPIRou and TESS reveal a super-Earth in a temperate orbit transiting an M4 dwarf
• Hubble Space Telescope transmission spectroscopy for the temperate sub-Neptune TOI-270d: a possible hydrogen-rich atmosphere containing water vapour
• New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State
• Shallower radius valley around low-mass hosts: Evidence for icy planets, collisions or high-energy radiation scatter
• The HD 260655 system: Two rocky worlds transiting a bright M dwarf at 10 pc
• A super-Earth and a mini-Neptune near the 2:1 MMR straddling the radius valley around the nearby mid-M dwarf TOI-2096
• HD 191939 revisited: New and refined planet mass determinations, and a new planet in the habitable zone
• The Demographics of Terrestrial Planets in the Venus Zone
• TOI-1695 b: A Water World Orbiting an Early M Dwarf in the Planet Radius Valley
• Characterising Atmospheres of Cloudy Temperate Mini-Neptunes with JWST
• TESS discovery of a sub-Neptune orbiting a mid-M dwarf TOI-2136
• JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-776b
• TOI-2046b, TOI-1181b and TOI-1516b, three new hot Jupiters from \textit{TESS}: planets orbiting a young star, a subgiant and a normal star
• TOI-1268b: the youngest, hot, Saturn-mass transiting exoplanet
• The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS
• Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40
• The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc
• TOI-1075 b: A Dense, Massive, Ultra-Short Period Hot Super-Earth Straddling the Radius Gap
• The Atmospheres of Rocky Exoplanets II. Influence of surface composition on the diversity of cloud condensates
• Hot planets around cool stars -- two short-period mini-Neptunes transiting the late K-dwarf TOI-1260
• TESS discovery of a super-Earth orbiting the M dwarf star TOI-1680
• Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf
• Planetary companions orbiting the M dwarfs GJ 724 and GJ 3988. A CARMENES and IRD collaboration
• The Terrestrial Planet Formation around M Dwarfs: In-situ, Inward Migration or Reversed Migration
• Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap
• A hot mini-Neptune and a temperate, highly eccentric sub-Saturn around the bright K-dwarf TOI-2134
• Abundance analysis of benchmark M dwarfs
• No Robust Statistical Evidence for a Population of Water Worlds in a 2025 Sample of Planets Orbiting M Stars
• TOI-1634 b: an Ultra-Short Period Keystone Planet Sitting Inside the M Dwarf Radius Valley
• Using observations of escaping H/He to constrain the atmospheric composition of sub-Neptunes