GJ 806 (TOI-4481): A bright nearby multi-planetary system with a transiting hot, low-density super-Earth

Abstract

One of the main scientific goals of the TESS mission is the discovery of transiting small planets around the closest and brightest stars in the sky. Here, using data from the CARMENES, MAROON-X, and HIRES spectrographs, together with TESS, we report the discovery and mass determination of a planetary system around the M1.5 V star GJ 806 (TOI-4481). GJ 806 is a bright (V=10.8 mag, J=7.3 mag) and nearby (d=12 pc) M dwarf that hosts at least two planets. The innermost planet, GJ 806 b, is transiting and has an ultra-short orbital period of 0.93 d, a radius of 1.331+-0.023 Re, a mass of 1.90+-0.17 Me, a mean density of 4.40+-0.45 g/cm3, and an equilibrium temperature of 940+-10 K. We detect a second, non-transiting, super-Earth planet in the system, GJ 806c, with an orbital period of 6.6 d, a minimum mass of 5.80+-0.30 Me, and an equilibrium temperature of 490+-5 K. The radial velocity data also shows evidence for a third periodicity at 13.6 d, although the current dataset does not provide sufficient evidence to unambiguously distinguish between a third super-Earth mass (Msin(i)=8.50+-0.45 Me) planet or stellar activity. Additionally, we report one transit observation of GJ 806 b taken with CARMENES in search for a possible extended atmosphere of H or He, but we can only place upper limits to its existence. This is not surprising as our evolutionary models support the idea that any possible primordial H/He atmosphere that GJ 806 b might have had, would long have been lost. However, GJ 806b's bulk density makes it likely that the planet hosts some type of volatile atmosphere. In fact, with a transmission spectroscopy metrics (TSM) of 44 and an emission spectroscopy metrics (ESM) of 24, GJ 806 b the third-ranked terrestrial planet around an M dwarf suitable for transmission spectroscopy studies, and the most promising terrestrial planet for emission spectroscopy studies.

arXiv commentUnder second review in A&A. This paper is NOT yet accepted, but it is made openly available to the community due to the approaching JWST deadline

References in corpus (105)

• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Transiting Exoplanet Survey Satellite
• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
• Las Cumbres Observatory Global Telescope Network
• Gaia Early Data Release 3: The astrometric solution
• The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)
• batman: BAsic Transit Model cAlculatioN in Python
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• Fast and scalable Gaussian process modeling with applications to astronomical time series
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• The stellar activity-rotation relationship and the evolution of stellar dynamos
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves (Expanded Edition)
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves
• Radial Velocities for 889 Late-type Stars
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• Growth Model Interpretation of Planet Size Distribution
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• Chromospheric CaII Emission in Nearby F, G, K, and M stars
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• RadVel: The Radial Velocity Modeling Toolkit
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey
• Late-type stars members of young stellar kinematic groups - I. Single stars
• Estimation of the XUV radiation onto close planets and their evaporation
• A Catalog of Northern Stars With Annual Proper Motions Larger Than 0.15 Seconds of Arc (LSPM catalog - North)
• Stellar and substellar companions of nearby stars from Gaia DR2 - Binarity from proper motion anomaly
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• Juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems
• Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• Finding extraterrestrial life using ground-based high-resolution spectroscopy
• Hot super-Earths stripped by their host stars
• Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1
• The CARMENES search for exoplanets around M dwarfs: High-resolution optical and near-infrared spectroscopy of 324 survey stars
• A Study of the Shortest-Period Planets Found With Kepler
• Photoevaporation and High-Eccentricity Migration Created the Sub-Jovian Desert
• PyTransit: Fast and Easy Exoplanet Transit Modelling in Python
• LDTk: Limb Darkening Toolkit
• A short-period censor of sub-Jupiter mass exoplanets with low density
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• The CARMENES search for exoplanets around M dwarfs: Different roads to radii and masses of the target stars
• CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS
• The New Generation Planetary Population Synthesis (NGPPS). I. Bern global model of planet formation and evolution, model tests, and emerging planetary systems
• A public HARPS radial velocity database corrected for systematic errors
• Magnetism, rotation, and nonthermal emission in cool stars -- Average magnetic field measurements in 292 M dwarfs
• Gaia Data Release 2: The catalogue of radial velocity standard stars
• Born Dry in the Photo-Evaporation Desert: Kepler's Ultra-Short-Period Planets Formed Water-Poor
• CARMENES input catalogue of M dwarfs V. Luminosities, colours, and spectral energy distributions
• Transiting extrasolar planetary candidates in the Galactic bulge
• Coherent radio emission from a quiescent red dwarf indicative of star-planet interaction
• The New Generation Planetary Population Synthesis (NGPPS). II. Planetary population of solar-like stars and overview of statistical results
• Flat-relative optimal extraction. A quick and efficient algorithm for stabilised spectrographs
• The L 98-59 System: Three Transiting, Terrestrial-Sized Planets Orbiting a Nearby M-dwarf
• Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization
• The CARMENES search for exoplanets around M dwarfs. Activity indicators at visible and near-infrared wavelengths
• CARMENES input catalogue of M dwarfs IV. New rotation periods from photometric time series
• The CARMENES search for exoplanets around M dwarfs. Stellar atmospheric parameters of target stars with SteParSyn
• Warm terrestrial planet with half the mass of Venus transiting a nearby star
• Revised mass-radius relationships for water-rich rocky planets more irradiated than the runaway greenhouse limit
• A new class of Super-Earths formed from high-temperature condensates: HD219134 b, 55 Cnc e, WASP-47 e
• The New Generation Planetary Population Synthesis (NGPPS). III. Warm super-Earths and cold Jupiters: A weak occurrence correlation, but with a strong architecture-composition link
• The CARMENES search for exoplanets around M dwarfs -- Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines
• Multicolour photometry for exoplanet candidate validation
• A He I upper atmosphere around the warm Neptune GJ 3470b
• Identifying Atmospheres on Rocky Exoplanets Through Inferred High Albedo
• 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
• A nearby transiting rocky exoplanet that is suitable for atmospheric investigation
• GJ 367b: A dense ultra-short period sub-Earth planet transiting a nearby red dwarf star
• Monitoring the radio emission of Proxima Centauri
• The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra
• Exoplanet-induced radio emission from M-dwarfs
• The sub-Neptune desert and its dependence on stellar type: Controlled by lifetime X-ray irradiation
• From Hot Jupiters to Super-Earths via Roche Lobe Overflow
• Detection of an Atmosphere on a Rocky Exoplanet
• RV-detected planets around M dwarfs: Challenges for core accretion models
• The New Generation Planetary Population Synthesis (NGPPS). V. Predetermination of planet types in global core accretion models
• A tentative detection of He I in the atmosphere of GJ 1214b
• From cold to hot irradiated gaseous exoplanets: Fingerprints of chemical disequilibrium in atmospheric spectra
• A Second Planet Transiting LTT 1445A and a Determination of the Masses of Both Worlds
• A detailed analysis of the Gl 486 planetary system
• GJ 1252 b: A 1.2 $R_{\oplus }$ planet transiting an M3-dwarf at 20.4 pc
• The New Generation Planetary Population Synthesis (NGPPS). VI. Introducing KOBE: Kepler Observes Bern Exoplanets. Theoretical perspectives on the architecture of planetary systems: Peas in a pod
• TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
• An ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685
• From cold to hot irradiated gaseous exoplanets: Toward an observation-based classification scheme
• Discovery of a hot, transiting, Earth-sized planet and a second temperate, non-transiting planet around the M4 dwarf GJ 3473 (TOI-488)
• Pushing planets into an inner cavity by a resonant chain
• The CARMENES search for exoplanets around M dwarfs. Period search in H$\alpha$, Na I D, and Ca II IRT lines
• Mass and density of the transiting hot and rocky super-Earth LHS 1478 b (TOI-1640 b)
• The CARMENES search for exoplanets around M dwarfs: Benchmarking the impact of activity in high-precision radial velocity measurements
• The role of clouds on the depletion of methane and water dominance in the transmission spectra of irradiated exoplanets
• Phase curve pollution of exoplanet transmission spectra
• The CARMENES search for exoplanets around M dwarfs: Two Saturn-mass planets orbiting active stars
• A transiting, temperate mini-Neptune orbiting the M dwarf TOI-1759 unveiled by TESS
• The Detection of Earth-mass Planets around Active Stars: The Mass of Kepler-78b
• Going back to basics: accelerating exoplanet transit modelling using Taylor-series expansion of the orbital motion
• On the origin of dynamically isolated hot Earths
• RoadRunner: a fast and flexible exoplanet transit model
• A multi-planetary system orbiting the early-M dwarf TOI-1238

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• Population-level Hypothesis Testing with Rocky Planet Emission Data: A Tentative Trend in the Brightness Temperatures of M-Earths
• TOI-4438 b: a transiting mini-Neptune amenable to atmospheric characterization
• The CARMENES search for exoplanets around M dwarfs. Revisiting the GJ 581 multi-planetary system with new Doppler measurements from CARMENES, HARPS, and HIRES
• No Robust Statistical Evidence for a Population of Water Worlds in a 2025 Sample of Planets Orbiting M Stars
• Discovery of a transiting hot water-world candidate orbiting Ross 176 with TESS and CARMENES
• TOI-4552 b: A new ultra-short period rocky world revealed by NIRPS and TESS
• A Search for helium in the atmospheres of three sub-Neptunes and a super-Earth around M-dwarfs