The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc

Abstract

We present the TESS discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright ($V_J$=12.5, $K_s$=8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70$\pm$0.04 $R_{\oplus }$ and 0.98$\pm$0.06 $R_{\oplus }$ in 0.86-day and 3.69-day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. HARPS RV monitoring yields 97.7 percentile mass upper limits of 0.35 $M_{\oplus }$ and 1.4 $M_{\oplus }$ for planets b and c, respectively. The astrometric companion detected by the CTIO/SMARTS 0.9m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the JWST and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9$\pm$0.1 $R_{\oplus }$ in a 4.97-day orbit is also identified in multi-Cycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung-Russell diagram. This gap is tied to the transition from partially- to fully-convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars.

arXiv commentPublished in The Astronomical Journal (31 pages, 21 figures, 11 tables, 3 appendices)

References in corpus (182)

• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Gaia mission
• The Transiting Exoplanet Survey Satellite
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• The SIMBAD astronomical database
• Analytic Lightcurves for Planetary Transit Searches
• Gaia Data Release 2: The astrometric solution
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The VizieR database of Astronomical Catalogues
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945
• Las Cumbres Observatory Global Telescope Network
• Gaia Early Data Release 3: The astrometric solution
• The NextGen Model Atmosphere grid for $3000\le \Teff \le 10000\K$
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• Fast and scalable Gaussian process modeling with applications to astronomical time series
• The Revised TESS Input Catalog and Candidate Target List
• A box-fitting algorithm in the search for periodic transits
• Models of Stars, Brown Dwarfs and Exoplanets
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Gaia Early Data Release 3: Photometric content and validation
• Most 1.6 Earth-Radius Planets are not Rocky
• Architecture and Dynamics of Kepler's Candidate Multiple Transiting Planet Systems
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• The TESS Input Catalog and Candidate Target List
• 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
• The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample
• The Occurrence Rate of Small Planets around Small Stars
• Probabilistic Forecasting of the Masses and Radii of Other Worlds
• The SuperCOSMOS Sky Survey. Paper I: Introduction and Description
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• Growth Model Interpretation of Planet Size Distribution
• New Neighbors from 2MASS: Activity and Kinematics at the Bottom of the Main Sequence
• The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• Design Considerations for a Ground-based Transit Search for Habitable Planets Orbiting M dwarfs
• Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• Metallicity and Temperature Indicators in M dwarf K band Spectra: Testing New & Updated Calibrations With Observations of 133 Solar Neighborhood M dwarfs
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• How to Constrain Your M dwarf II: the mass-luminosity-metallicity relation from 0.075 to 0.70$M_{\odot }$
• M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale
• A temperate rocky super-Earth transiting a nearby cool star
• Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars
• Extracting Planet Mass and Eccentricity From TTV data
• STARRY: Analytic Occultation Light Curves
• Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes
• Kepler Data Validation I -- Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates
• Almost All of Kepler's Multiple Planet Candidates are Planets
• Was Venus the First Habitable World of our Solar System?
• Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
• CHIRON - A Fiber Fed Spectrometer for Precise Radial Velocities
• Proxima's orbit around Alpha Centauri
• Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1
• Kepler Data Validation II -- Transit Model Fitting and Multiple-Planet Search
• Real-time processing of the imaging data from the network of Las Cumbres Observatory Telescopes using BANZAI
• Transit Least Squares: Optimized transit detection algorithm to search for periodic transits of small planets
• Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b
• A planet within the debris disk around the pre-main-sequence star AU Microscopii
• SOAR TESS Survey. I: Sculpting of TESS planetary systems by stellar companions
• A rocky planet transiting a nearby low-mass star
• Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC 2423 and NGC 4349
• The inner edge of the habitable zone for synchronously rotating planets around low-mass stars using general circulation models
• A resonant chain of four transiting, sub-Neptune planets
• Planetary Candidates from the First Year of the K2 Mission
• The Solar Neighborhood XXXVII: The Mass-Luminosity Relation for Main Sequence M Dwarfs
• Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era
• Overstable Librations can account for the Paucity of Mean Motion Resonances among Exoplanet Pairs
• The CARMENES search for exoplanets around M dwarfs: Different roads to radii and masses of the target stars
• Prospecting in late-type dwarfs: a calibration of infrared and visible spectroscopic metallicities of late-K and M dwarfs spanning 1.5 dex
• Transit Timing Observations from Kepler: VII. Confirmation of 27 planets in 13 multiplanet systems via Transit Timing Variations and orbital stability
• Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK
• Ten years of speckle interferometry at SOAR
• Empirical, Accurate Masses and Radii of Single Stars with TESS and Gaia
• A Rocky Composition for an Earth-sized Exoplanet
• Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type
• 275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0-10
• The ASAS-SN Catalog of Variable Stars III: Variables in the Southern TESS Continuous Viewing Zone
• Venusian Habitable Climate Scenarios: Modeling Venus through time and applications to slowly rotating Venus-Like Exoplanets
• Transits and Occultations of an Earth-Sized Planet in an 8.5-Hour Orbit
• TESS Discovery of an ultra-short-period planet around the nearby M dwarf LHS 3844
• Analytic Planetary Transit Light Curves and Derivatives for Stars with Polynomial Limb Darkening
• The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293
• Minimum Radii of Super-Earths: Constraints from Giant Impacts
• The Solar Neighborhood XXXV: Distances to 1404 M Dwarf Systems Within 25 pc in the Southern Sky
• The Solar Neighborhood XXXII. The Hydrogen Burning Limit
• The Solar Neighborhood X: New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs
• Magnetospheric Truncation, Tidal Inspiral, and the Creation of Short and Ultra-Short Period Planets
• Local Stellar Kinematics from RAVE Data: I. Local Standard of Rest
• The L 98-59 System: Three Transiting, Terrestrial-Sized Planets Orbiting a Nearby M-dwarf
• TESS Spots a Compact System of Super-Earths around the Naked-Eye Star HR 858
• Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization
• A super-Earth and two sub-Neptunes transiting the nearby and quiet M dwarf TOI-270
• Are Planetary Systems Filled to Capacity? A Study Based on Kepler Results
• Kepler-78 and the Ultra-Short-Period Planets
• Revisiting Proxima with ESPRESSO
• The Solar Neighborhood XIII: Parallax Results from the CTIOPI 0.9-m Program -- Stars with mu >= 1"/year (MOTION Sample)
• New constraints on the planetary system around the young active star AU Mic. Two transiting warm Neptunes near mean-motion resonance
• The Solar Neighborhood VI: New Southern Stars Identified by Optical Spectroscopy
• A Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite
• Warm terrestrial planet with half the mass of Venus transiting a nearby star
• Convergent Migration Renders TRAPPIST-1 Long-lived
• On the Frequency of Potential Venus Analogs from Kepler Data
• The First Habitable Zone Earth-sized Planet from TESS. I: Validation of the TOI-700 System
• Venus as a Laboratory for Exoplanetary Science
• A second terrestrial planet orbiting the nearby M dwarf LHS 1140
• A super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266
• The Solar Neighborhood. XXI. Parallax Results from the CTIOPI 0.9m Program: 20 New Members of the 25 Parsec White Dwarf Sample
• Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs
• A pair of TESS planets spanning the radius valley around the nearby mid-M dwarf LTT 3780
• Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky Data Release
• The Lowest Mass White Dwarf
• Homogeneous Analysis of Hot Earths: Masses, Sizes, and Compositions
• The Solar Neighborhood XLIX: Nine Giant Planets Orbiting Nearby K Dwarfs, and the CHIRON Spectrograph's Radial Velocity Performance
• Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley
• Planetary system LHS 1140 revisited with ESPRESSO and TESS
• A Criterion for the Onset of Chaos in Systems of Two Eccentric Planets
• Meeting the Cool Neighbors VII: Spectroscopy of faint, red NLTT dwarfs
• 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 Gap in the Lower Main Sequence Revealed by Gaia Data Release 2
• A nearby transiting rocky exoplanet that is suitable for atmospheric investigation
• Characterization of the L 98-59 multi-planetary system with HARPS: two confirmed terrestrial planets and a mass upper limit on the third
• Radial velocity follow-up of GJ1132 with HARPS. A precise mass for planet 'b' and the discovery of a second planet
• Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES
• 44 Validated Planets from K2 Campaign 10
• The Densities of Planets in Multiple Stellar Systems
• Detection of Hundreds of New Planet Candidates and Eclipsing Binaries in K2 Campaigns 0-8
• The Quasiperiodic Automated Transit Search Algorithm
• Discovery and Vetting of Exoplanets I: Benchmarking K2 Vetting Tools
• The Solar Neighborhood. XXXIX. Parallax Results from the CTIOPI and NOFS Programs: 50 New Members of the 25 Parsec White Dwarf Sample
• A super-Earth and sub-Neptune transiting the late-type M dwarf LP 791-18
• Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars I: Classifying Low-mass Host Stars Observed During Campaigns 1-7
• A hot terrestrial planet orbiting the bright M dwarf L 168-9 unveiled by TESS
• Radii of 88 M Subdwarfs and Updated Radius Relations for Low-Metallicity M Dwarf Stars
• A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776
• The Dynamics of the Multi-planet System Orbiting Kepler-56
• A closer look at the transition between fully convective and partly radiative low mass stars
• A 3D Search for Companions to 12 Nearby M-Dwarfs
• Secular Dynamics of an Exterior Test Particle: The Inverse Kozai and Other Eccentricity-Inclination Resonances
• SOAR Adaptive Module (SAM): seeing improvement with a UV laser
• Orbital Dynamics of Multi-Planet Systems with Eccentricity Diversity
• The CARMENES search for exoplanets around M dwarfs -- LP 714-47b (TOI 442.01): Populating the Neptune desert
• A He3 driven instability near the fully convective boundary
• GJ 1252 b: A 1.2 $R_{\oplus }$ planet transiting an M3-dwarf at 20.4 pc
• Chi-Square Discriminators for Transiting Planet Detection in Kepler Data
• TOI-1235 b: a keystone super-Earth for testing radius valley emergence models around early M dwarfs
• An ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685
• Discovery of a hot, transiting, Earth-sized planet and a second temperate, non-transiting planet around the M4 dwarf GJ 3473 (TOI-488)
• The Five Planets in the Kepler-296 Binary System All Orbit the Primary: A Statistical and Analytical Analysis
• An Integrable Model for the Dynamics of Planetary Mean Motion Resonances
• TOI-674b: an oasis in the desert of exo-Neptunes transiting a nearby M dwarf
• A warm Jupiter transiting an M dwarf: A TESS single transit event confirmed with the Habitable-zone Planet Finder
• Mass and density of the transiting hot and rocky super-Earth LHS 1478 b (TOI-1640 b)
• Gaia Gaps and the Physics of Low-Mass Stars. I. The Fully Convective Boundary
• LHS 1815b: The First Thick-Disk Planet Detected By TESS
• The Solar Neighborhood XXXVIII. Results from the CTIO/SMARTS 0.9m: Trigonometric Parallaxes for 151 Nearby M Dwarf Systems
• Eccentricity Driven Climate Effects in the Kepler-1649 System
• TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399
• An explanation for the gap in the Gaia HRD for M dwarfs
• TOI-1728b: The Habitable-zone Planet Finder confirms a warm super Neptune orbiting an M dwarf host
• TOI-532b: The Habitable-zone Planet Finder confirms a Large Super Neptune in the Neptune Desert orbiting a metal-rich M dwarf host
• TOI 540 b: A Planet Smaller than Earth Orbiting a Nearby Rapidly Rotating Low-mass Star
• Spectroscopic Orbits of Eleven Nearby, Mid-to-Late M Dwarf Binaries
• In the Presence of a Wrecking Ball: Orbital Stability in the HR 5183 System
• Orbital Stability and Precession Effects in the Kepler-89 System
• K2-288Bb: A Small Temperate Planet in a Low-mass Binary System Discovered by Citizen Scientists
• Characterisation of 92 Southern TESS Candidate Planet Hosts and a New Photometric [Fe/H] Relation for Cool Dwarfs
• TOI 122b and TOI 237b, two small warm planets orbiting inactive M dwarfs, found by \textit{TESS}
• The Solar Neighborhood XLII. Parallax Results from the CTIOPI 0.9-m Program --- Identifying New Nearby Subdwarfs Using Tangential Velocities and Locations on the H-R Diagram
• TOI-1749: an M dwarf with a Trio of Planets including a Near-Resonant Pair
• Two Bright M Dwarfs Hosting Ultra-Short-Period Super-Earths with Earth-like Compositions
• TOI-1634 b: an Ultra-Short Period Keystone Planet Sitting Inside the M Dwarf Radius Valley

Cited by in corpus (10)

• TOI-5205 b: A Short-period Jovian Planet Transiting a Mid-M Dwarf
• The Discovery of a Planetary Companion Interior to Hot Jupiter WASP-132 b
• TOI-3235 b: a transiting giant planet around an M4 dwarf star
• TOI-1442 b and TOI-2445 b: two potentially rocky ultra-short period planets around M dwarfs
• The Solar Neighborhood LI: A Variability Survey of Nearby M Dwarfs with Planets from Months to Decades with TESS and the CTIO/SMARTS 0.9 m Telescope
• Two warm Earth-sized exoplanets and an Earth-sized candidate in the M5V-M6V binary system TOI-2267
• exoMMR: a New Python Package to Confirm and Characterize Mean Motion Resonances
• Validation of a Third Planet in the LHS 1678 System
• TFAW survey II: 6 Newly Validated Planets and 13 Planet Candidates from K2
• Upper Limits on Planet-Induced GHz Radio Emission from Inactive M Dwarfs