A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654

Abstract

We report the discovery and Doppler mass measurement of a 7.4-day 2.3-$R_{\oplus }$ mini-Neptune around a metal-poor K dwarf BD+29 2654 (TOI-2018). Based on a high-resolution Keck/HIRES spectrum, the Gaia parallax, and multi-wavelength photometry from the ultraviolet to the mid-infrared, we found that the host star has $T_{\text{eff}}=4174_{-42}^{+34}$ K, $\log g=4.62_{-0.03}^{+0.02}$, $[\text{Fe/H}]=-0.58\pm 0.18$, $M_{\ast }=0.57\pm 0.02M_{\odot }$, and $R_{\ast }=0.62\pm 0.01R_{\odot }$. Precise Doppler measurements with Keck/HIRES revealed a planetary mass of $M_{\text{p}}=9.2\pm 2.1M_{\oplus }$ for TOI-2018 b. TOI-2018 b has a mass and radius that are consistent with an Earth-like core with a $\sim 1\%$-by-mass hydrogen/helium envelope, or an ice-rock mixture. The mass of TOI-2018 b is close to the threshold for run-away accretion and hence giant planet formation. Such a threshold is predicted to be around 10$M_{\oplus }$ or lower for a low-metallicity (low-opacity) environment. If TOI-2018 b is a planetary core that failed to undergo run-away accretion, it may underline the reason why giant planets are rare around low-metallicity host stars (one possibility is their shorter disk lifetimes). With a K-band magnitude of 7.1, TOI-2018 b may be a suitable target for transmission spectroscopy with the James Webb Space Telescope. The system is also amenable to metastable Helium observation; the detection of a Helium exosphere would help distinguish between a H/He enveloped planet and a water world.

arXiv comment10 figures, 5 tables, accepted to AAS Journals

References in corpus (107)

• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• Gaia Data Release 3: Summary of the content and survey properties
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The James Webb Space Telescope
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The WASP Project and the SuperWASP Cameras
• Gaia Early Data Release 3: The astrometric solution
• 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
• The Revised TESS Input Catalog and Candidate Target List
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• A box-fitting algorithm in the search for periodic transits
• Spectroscopic [Fe/H] for 98 extra-solar planet-host stars: Exploring the probability of planet formation
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• Prevalence of Earth-size planets orbiting Sun-like stars
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Most 1.6 Earth-Radius Planets are not Rocky
• The evaporation valley in the Kepler planets
• Gaia Data Release 2: Photometric content and validation
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Planet-disk interaction and orbital evolution
• The chemical make-up of the Sun: A 2020 vision
• Rotation Periods of 34,030 Kepler Main-Sequence Stars: The Full Autocorrelation Sample
• 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
• The GALAH+ Survey: Third Data Release
• Gaia Data Release 2: Catalogue validation
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• Growth Model Interpretation of Planet Size Distribution
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• BANYAN. XI. The BANYAN $\Sigma$ multivariate Bayesian algorithm to identify members of young associations within 150 pc
• Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• Core-powered mass loss and the radius distribution of small exoplanets
• The Thirteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey MApping Nearby Galaxies at Apache Point Observatory
• Mass-Radius Relation for Rocky Planets based on PREM
• Gaia Early Data Release 3 -- Catalogue validation
• The California Planet Survey I. Four New Giant Exoplanets
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• Helium in the eroding atmosphere of an exoplanet
• The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets
• Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller
• Atmospheres of protoplanetary cores: critical mass for nucleated instability
• 3D maps of the local ISM from inversion of individual color excess measurements
• Modern stellar spectroscopy caveats
• Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• Three-dimensional mapping of the local interstellar medium with composite data
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• To Cool is to Accrete: Analytic Scalings for Nebular Accretion of Planetary Atmospheres
• SOAR TESS Survey. I: Sculpting of TESS planetary systems by stellar companions
• A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium
• Evolutionary Analysis of Gaseous Sub-Neptune-Mass Planets with MESA
• Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era
• A Guide to Realistic Uncertainties on Fundamental Properties of Solar-Type Exoplanet Host Stars
• 3D maps of interstellar dust in the Local Arm: using $Gaia$, 2MASS and APOGEE-DR14
• Revealing A Universal Planet-Metallicity Correlation For Planets of Different Sizes Around Solar-Type Stars
• PALM-3000: Exoplanet Adaptive Optics for the 5-meter Hale Telescope
• The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities
• Determining the Mass of Kepler-78b With Nonparametric Gaussian Process Estimation
• Gaia Data Release 2: processing of the photometric data
• Metallicity, planet formation, and disc lifetimes
• Mass-radius relationships for irradiated ocean planets
• Stellar Mass Dependent Disk Dispersal
• Helium Absorption at 1083 nm from Extended Exoplanet Atmospheres: Dependence on Stellar Radiation
• Warm terrestrial planet with half the mass of Venus transiting a nearby star
• The GALAH survey: effective temperature calibration from the InfraRed Flux Method in the Gaia system
• Multicolour photometry for exoplanet candidate validation
• Gaia Early Data Release 3. Building the Gaia DR3 source list -- Cross-match of Gaia observations
• The Empirical Limits of Gyrochronology
• The Boundary between Gas-rich and Gas-poor Planets
• Short Lifetime of Protoplanetary Disks in Low-metallicity Environments
• Radiation Hydrodynamics Simulations of Photoevaporation of Protoplanetary Disks by Ultra Violet Radiation: Metallicity Dependence
• The discovery and mass measurement of a new ultra-short-period planet: EPIC~228732031b
• A pair of Sub-Neptunes transiting the bright K-dwarf TOI-1064 characterised with CHEOPS
• Evidence for the volatile-rich composition of a 1.5-$R_{\oplus }$ planet
• Gaia Search for stellar Companions of TESS Objects of Interest
• The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515
• Compact multi-planet systems are more common around metal poor hosts
• Metastable Helium Absorptions with 3D Hydrodynamics and Self-Consistent Photochemistry I: WASP-69b, Dimensionality, XUV Flux Level, Spectral Types, and Flares
• Evidence that the Hot Jupiter WASP-77 A b Formed Beyond Its Parent Protoplanetary Disk's H2O Ice Line
• ShaneAO: wide science spectrum adaptive optics system for the Lick Observatory
• TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes
• HIP 114328: a new refractory-poor and Li-poor solar twin
• TOI-561 b: A Low Density Ultra-Short Period "Rocky" Planet around a Metal-Poor Star
• AstraLux - the Calar Alto 2.2-m telescope Lucky Imaging camera
• Gaia Data Release 2. Calibration and mitigation of electronic offset effects in the data
• Gaia Search for stellar Companions of TESS Objects of Interest II
• Optically Thin Core Accretion: How Planets Get Their Gas in Nearly Gas-Free Disks
• Know thy star, know thy planet: Chemo-kinematically characterizing TESS targets
• Three Pathways for Observed Resonant Chains
• Commissioning ShARCS: the Shane Adaptive optics infraRed Camera-Spectrograph for the Lick Observatory 3-m telescope
• Gaia Search for stellar Companions of TESS Objects of Interest III

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• Shallower radius valley around low-mass hosts: Evidence for icy planets, collisions or high-energy radiation scatter
• The MOPYS project: A survey of 70 planets in search of extended He I and H atmospheres. No evidence of enhanced evaporation in young planets
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• Which stars can form planets: Planetesimal formation at low metallicities
• Helium escape signatures are generally strongest during younger ages but this age dependence is lost in the diversity of observed exoplanets
• Characterizing planetary systems with SPIRou: Detection of a sub-Neptune in a 6-day period orbit around the M dwarf Gl 410