The TESS-Keck Survey II: An Ultra-Short Period Rocky Planet and its Siblings Transiting the Galactic Thick-Disk Star TOI-561

Abstract

We report the discovery of TOI-561, a multi-planet system in the galactic thick disk that contains a rocky, ultra-short period planet (USP). This bright ($V=10.2$) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P=0.44 days, $R_b=1.45\pm 0.11R_{\oplus }$), c (TOI-561.01, P=10.8 days, $R_c=2.90\pm 0.13R_{\oplus }$), and d (TOI-561.03, P=16.3 days, $R_d=2.32\pm 0.16R_{\oplus }$). The star is chemically ([Fe/H]$=-0.41\pm 0.05$, [$\alpha$/H]$=+0.23\pm 0.05$) and kinematically consistent with the galactic thick disk population, making TOI-561 one of the oldest ($10\pm 3$Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of $3.2\pm 0.8M_{\oplus }$ and $5.5_{-1.6}^{+2.0}$gcm${}^{-3}$, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is $7.0\pm 2.3M_{\oplus }$ and $1.6\pm 0.6$gcm${}^{-3}$, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.

arXiv commentAccepted at The Astronomical Journal; 25 pages, 10 figures

References in corpus (103)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Transiting Exoplanet Survey Satellite
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Gaia Data Release 2: The astrometric solution
• Las Cumbres Observatory Global Telescope Network
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• The false positive rate of Kepler and the occurrence of planets
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• batman: BAsic Transit Model cAlculatioN in Python
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Prevalence of Earth-size planets orbiting Sun-like stars
• The GALAH Survey: Scientific Motivation
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Most 1.6 Earth-Radius Planets are not Rocky
• Chemical evolution with radial mixing
• An absolutely calibrated effective temperature scale from the InfraRed Flux Method
• 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 (Expanded Edition)
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• Growth Model Interpretation of Planet Size Distribution
• Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program.Galactic stellar populations and planets
• RadVel: The Radial Velocity Modeling Toolkit
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• Simulations of Galaxy Formation in a Lambda CDM Universe I: Dynamical and Photometric Properties of a Simulated Disk Galaxy
• The California Planet Survey I. Four New Giant Exoplanets
• Weakened magnetic braking as the origin of anomalously rapid rotation in old field stars
• Spectroscopy Made Easy: Evolution
• The Emergence of the Thick Disk in a CDM Universe
• Origin and structure of the Galactic disc(s)
• Spectral Properties of Cool Stars: Extended Abundance Analysis of 1617 Planet Search Stars
• Extracting Planet Mass and Eccentricity From TTV data
• Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes
• The California-Kepler Survey V. Peas in a Pod: Planets in a Kepler Multi-planet System are Similar in Size and Regularly Spaced
• Kepler Data Validation I -- Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• A simple method to estimate radial velocity variations due to stellar activity using photometry
• Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
• A map of the large day-night temperature gradient of a super-Earth exoplanet
• Stellar Abundances in the Solar Neighborhood: The Hypatia Catalog
• Limits on Planetary Companions from Doppler Surveys of Nearby Stars
• The Next Generation Transit Survey (NGTS)
• The Milky Way has no thick disk
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• The orbital eccentricity of small planet systems
• A Study of the Shortest-Period Planets Found With Kepler
• 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
• Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b
• SOAR TESS Survey. I: Sculpting of TESS planetary systems by stellar companions
• An ancient extrasolar system with five sub-Earth-size planets
• Oxygen trends in the Galactic thin and thick disks
• Fast Star, Slow Star; Old Star, Young Star: Subgiant Rotation as a Population and Stellar Physics Diagnostic
• The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
• Born Dry in the Photo-Evaporation Desert: Kepler's Ultra-Short-Period Planets Formed Water-Poor
• Confirming chemical clocks: asteroseismic age dissection of the Milky Way disk(s)
• Determining the Mass of Kepler-78b With Nonparametric Gaussian Process Estimation
• Minimum Radii of Super-Earths: Constraints from Giant Impacts
• Detection of Thermal Emission from a Super-Earth
• The Roche limit for close-orbiting planets: Minimum density, composition constraints, and application to the 4.2-hour planet KOI 1843.03
• The TESS-HERMES survey Data Release 1: high-resolution spectroscopy of the TESS southern continuous viewing zone
• Predicting the long-term stability of compact multiplanet systems
• Homogeneous Analysis of Hot Earths: Masses, Sizes, and Compositions
• Ultra-short-period planets from secular chaos
• Orbital Architectures of Planet-Hosting Binaries: I. Forming Five Small Planets in the Truncated Disk of Kepler-444A
• MuSCAT2: four-color Simultaneous Camera for the 1.52-m Telescopio Carlos Sánchez
• Low-Eccentricity Migration of Ultra-Short Period Planets in Multi-Planet Systems
• Larger mutual inclinations for the shortest-period planets
• CKS VIII: Eccentricities of Kepler Planets and Tentative Evidence of a High Metallicity Preference for Small Eccentric Planets
• Updated Parameters and a New Transmission Spectrum of HD 97658b
• Accurate Gravities of F, G, and K stars from High Resolution Spectra Without External Constraints
• Revised Masses and Densities of the Planets around Kepler-10
• Effects of Unseen Additional Planetary Perturbers on Compact Extrasolar Planetary Systems
• The discovery and mass measurement of a new ultra-short-period planet: EPIC~228732031b
• Chemical Evolution in the Milky Way: Rotation-based ages for APOGEE-Kepler cool dwarf stars
• An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561
• MuSCAT2 multicolour validation of TESS candidates: an ultra-short-period substellar object around an M dwarf
• DONUTS: A science frame autoguiding algorithm with sub-pixel precision, capable of guiding on defocused stars
• A hot terrestrial planet orbiting the bright M dwarf L 168-9 unveiled by TESS
• Simultaneous TESS and NGTS Transit Observations of WASP-166b
• The Photoeccentric Effect and Proto-Hot Jupiters II. KOI-1474.01, a candidate eccentric planet perturbed by an unseen companion
• A low stellar obliquity for WASP-47, a compact multiplanet system with a hot Jupiter and an ultra-short period planet
• Pinning down the mass of Kepler-10c: the importance of sampling and model comparison
• Speckle interferometry at SOAR in 2016 and 2017
• The TESS-Keck Survey I: A Warm Sub-Saturn-mass Planet and a Caution about Stray Light in TESS Cameras
• Ultra-short-period Planets are Stable Against Tidal Inspiral
• LHS 1815b: The First Thick-Disk Planet Detected By TESS
• Measuring oxygen abundances from stellar spectra without oxygen lines
• Know thy star, know thy planet: Chemo-kinematically characterizing TESS targets
• Mutual Inclination Excitation by Stellar Oblateness
• Shallow transit follow-up from NGTS: simultaneous observations of HD106315 with 11 identical telescopes

Cited by in corpus (29)

• The Ariel Target List: The Impact of TESS and the Potential for Characterising Multiple Planets Within a System
• A framework for the architecture of exoplanetary systems. I. Four classes of planetary system architecture
• TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes
• An unusually low-density super-Earth transiting the bright early-type M-dwarf GJ 1018 (TOI-244)
• Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N and TESS
• New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State
• TOI-561 b: A Low Density Ultra-Short Period "Rocky" Planet around a Metal-Poor Star
• The TESS-Keck Survey: Science Goals and Target Selection
• The TESS-Keck Survey. VIII. Confirmation of a Transiting Giant Planet on an Eccentric 261 day Orbit with the Automated Planet Finder Telescope
• TESS-Keck Survey IX: Masses of Three Sub-Neptunes Orbiting HD 191939 and the Discovery of a Warm Jovian Plus a Distant Sub-Stellar Companion
• Exoplanets in the Galactic context: Planet occurrence rates in the thin disk, thick disk and stellar halo of Kepler stars
• Generalized Peas-in-a-Pod: Extending Intra-System Mass Uniformity to Non-TTV Systems via the Gini Index
• The TESS-Keck Survey. XV. Precise Properties of 108 TESS Planets and Their Host Stars
• GJ 3090 b: one of the most favourable mini-Neptune for atmospheric characterisation
• TKS V. Twin sub-Neptunes Transiting the Nearby G Star HD 63935
• Migrating Planets into Ultra-Short-Period Orbits during Episodic Accretion Events
• The chemical evolution of the solar neighbourhood for planet-hosting stars
• TESS-Keck Survey XIV: Two giant exoplanets from the Distant Giants Survey
• GJ 3929: High Precision Photometric and Doppler Characterization of an Exo-Venus and its Hot, Mini-Neptune-mass Companion
• The AstraLux-TESS high-spatial resolution imaging survey. Search for stellar companions of 215 planet candidates from TESS
• CHEOPS and TESS view of the ultra-short period super-Earth TOI-561 b
• The GALAH Survey: Improving our understanding of confirmed and candidate planetary systems with large stellar surveys
• Searching for Hot Water World Candidates with CHEOPS: Refining the radii and analysing the internal structures and atmospheric lifetimes of TOI-238 b and TOI-1685 b
• TOI-3568 b: a super-Neptune in the sub-Jovian desert
• A Close-in Planet Orbiting Giant Star HD 167768
• The TESS-Keck Survey. XIX. A Warm Transiting Sub-Saturn Mass Planet and a non-Transiting Saturn Mass Planet Orbiting a Solar Analog
• Radius and mass distribution of ultra-short period planets
• The Occurrence-weighted Median Planets Discovered by Transit Surveys Orbiting Solar-type Stars and Their Implications for Planet Formation and Evolution
• The TESS-Keck Survey. XI. Mass Measurements for Four Transiting sub-Neptunes orbiting K dwarf TOI-1246