Separated twins or just siblings? A multi-planet system around an M dwarf including a cool sub-Neptune

Abstract

We report the discovery of two TESS sub-Neptunes orbiting the early M dwarf TOI-904 (TIC 261257684). Both exoplanets, TOI-904 b and c, were initially observed in TESS Sector 12 with twin sizes of ${2.426}_{-0.157}^{+0.163}$ and ${2.167}_{-0.118}^{+0.130}$ R${}_{\oplus }$, respectively. Through observations in five additional sectors in the TESS primary mission and the first and second extended missions, the orbital periods of the planets were measured to be 10.887$\pm$0.001 and 83.999$\pm$0.001 days, respectively. Reconnaissance radial velocity measurements (taken with EULER/CORALIE and SMARTS/CHIRON) and high-resolution speckle imaging with adaptive optics (obtained from SOAR/HRCAM and Gemini South/ZORRO) show no evidence of an eclipsing binary or a nearby companion, which, together with the low false-positive probabilities calculated with the statistical validation software TRICERATOPS, establishes the planetary nature of these candidates. The outer planet, TOI-904 c, is the longest-period M dwarf exoplanet found by TESS, with an estimated equilibrium temperature of 217 K. As the three other validated planets with comparable host stars and orbital periods were observed by Kepler around much dimmer stars (J mag > 12), TOI-904 c, orbiting a brighter star (J mag = 9.6), is the coldest M dwarf planet easily accessible for atmospheric follow-up. Future mass measurements and transmission spectroscopy of the similar-sized planets in this system could determine whether they are also similar in density and composition, suggesting a common formation pathway, or whether they have distinct origins.

18 pages, 6 figures, accepted by ApJL

References in corpus (79)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• 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 Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Gaia Data Release 3: Summary of the content and survey properties
• The Transiting Exoplanet Survey Satellite
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences
• Gaia Data Release 2: The astrometric solution
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• Las Cumbres Observatory Global Telescope Network
• batman: BAsic Transit Model cAlculatioN in Python
• The Revised TESS Input Catalog and Candidate Target List
• astroquery: An Astronomical Web-Querying Package in Python
• Gaia Early Data Release 3: Photometric content and validation
• 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)
• Probabilistic Forecasting of the Masses and Radii of Other Worlds
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• ESPRESSO@VLT -- On-sky performance and first results
• RadVel: The Radial Velocity Modeling Toolkit
• Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• False positive probabilties for all Kepler Objects of Interest: 1284 newly validated planets and 428 likely false positives
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• How to Constrain Your M dwarf II: the mass-luminosity-metallicity relation from 0.075 to 0.70$M_{\odot }$
• Juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems
• Revised Radii of Kepler Stars and Planets Using Gaia Data Release 2
• 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
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• Migration then assembly: Formation of Neptune mass planets inside 1 AU
• CHIRON - A Fiber Fed Spectrometer for Precise Radial Velocities
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• An Earth-sized Planet in the Habitable Zone of a Cool Star
• Parallax Systematics and Photocenter Motions of Benchmark Eclipsing Binaries in Gaia EDR3
• The Exoplanet Population Observation Simulator. I - The Inner Edges of Planetary Systems
• Real-time processing of the imaging data from the network of Las Cumbres Observatory Telescopes using BANZAI
• Kepler Data Validation II -- Transit Model Fitting and Multiple-Planet Search
• Wotan: Comprehensive time-series de-trending in Python
• eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
• Inside-Out Planet Formation
• LDTk: Limb Darkening Toolkit
• exoplanet: Gradient-based probabilistic inference for exoplanet data & other astronomical time series
• Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• Ten years of speckle interferometry at SOAR
• Empirical, Accurate Masses and Radii of Single Stars with TESS and Gaia
• Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type
• Characterizing the Cool Kepler Objects of Interest. New Effective Temperatures, Metallicities, Masses and Radii of Low-Mass Kepler Planet-Candidate Host Stars
• Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone
• Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization
• Architectures of Exoplanetary Systems. I: A Clustered Forward Model for Exoplanetary Systems around Kepler's FGK Stars
• The Precision of Mass Measurements Required for Robust Atmospheric Characterization of Transiting Exoplanets
• The Solar Neighborhood XLIX: Nine Giant Planets Orbiting Nearby K Dwarfs, and the CHIRON Spectrograph's Radial Velocity Performance
• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1-1000 AU and Implications for Small Planet Detection
• Planetary system LHS 1140 revisited with ESPRESSO and TESS
• Planet formation around low mass stars: the moving snow line and super-Earths
• 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 Densities of Planets in Multiple Stellar Systems
• Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters
• An Estimate of the Yield of Single-Transit Planetary Events from the Transiting Exoplanet Survey Satellite
• Orbital Parameter Determination for Wide Stellar Binary Systems in the Age of Gaia
• The Magellan PFS Planet Search Program: Radial Velocity and Stellar Abundance Analyses of the 360 AU, Metal-Poor Binary "Twins" HD 133131A & B
• The First Habitable Zone Earth-Sized Planet From TESS II: $Spitzer$ Confirms TOI-700 d
• The Five Planets in the Kepler-296 Binary System All Orbit the Primary: A Statistical and Analytical Analysis
• The Imprint of the Protoplanetary Disk in the Accretion of Super-Earth Envelopes
• A warm Jupiter transiting an M dwarf: A TESS single transit event confirmed with the Habitable-zone Planet Finder
• Validation of small Kepler transiting planet candidates in or near the habitable zone
• Hidden Worlds: Dynamical Architecture Predictions of Undetected Planets in Multi-planet Systems and Applications to TESS Systems
• K2-110 b - a massive mini-Neptune exoplanet
• TOI-2285b: A 1.7 Earth-radius Planet Near the Habitable Zone around a Nearby M Dwarf
• In Situ Models for Planet Assembly around Cool stars
• The Terrestrial Planet Formation around M Dwarfs: In-situ, Inward Migration or Reversed Migration

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