A Statistical Analysis of SEEDS and Other High-Contrast Exoplanet Surveys: Massive Planets or Low-Mass Brown Dwarfs?

Abstract

We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections ($\kappa$ And b, two $\sim$60 M${}_{\mathrm{J}}$ brown dwarf companions in the Pleiades, PZ Tel B, and CD$-$35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of $\sim$30--100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at $\sim$5 M${}_{\mathrm{Jup}}$, with a single power law distribution. We find that $p(M,a)\propto M^{-0.65\pm 0.60}{a}^{-0.85\pm 0.39}$ (1$\sigma$ errors) provides an adequate fit to our data, with 1.0--3.1\% (68\% confidence) of stars hosting 5--70 $M_{\mathrm{Jup}}$ companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

ApJ in press, replaced with accepted version. Methodology clarified, conclusions mostly unchanged

References in corpus (26)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Optical Images of an Exosolar Planet 25 Light Years from Earth
• On the Luminosity of Young Jupiters
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• Search for Associations Containing Young stars (SACY): I. Sample & Searching Method
• The Gemini Deep Planet Survey -- GDPS
• A New Planet Around an M Dwarf: Revealing a Correlation Between Exoplanets and Stellar Mass
• Spitzer IRS Spectroscopy of IRAS-Discovered Debris Disks
• The Two Modes of Gas Giant Planet Formation
• Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
• Patterns of photometric and chromospheric variation among Sun-like stars: A 20-year perspective
• The Palomar/Keck Adaptive Optics Survey of Young Solar Analogs: Evidence for a Universal Companion Mass Function
• Stellar Parameters and Metallicities of Stars Hosting Jovian and Neptunian Mass Planets: A Possible Dependence of Planetary Mass on Metallicity
• The nearest young moving groups
• The Distances to Open Clusters from Main-Sequence Fitting. III. Improved Accuracy with Empirically Calibrated Isochrones
• High-Dispersion Optical Spectra of Nearby Stars Younger Than The Sun
• The minimum mass for star formation, and the origin of binary brown dwarfs
• New periodic variable stars coincident with ROSAT sources discovered using SuperWASP
• Young Nearby Loose Associations
• On the kinematic evolution of young local associations and the Sco-Cen complex
• Rapid Formation of Icy Super-Earths and the Cores of Gas Giant Planets
• Deficit of wide binaries in the eta Chamaeleontis young cluster
• A discontinuity in the low-mass IMF - the case of high multiplicity
• The Minimum Jeans Mass, Brown Dwarf Companion IMF, and Predictions for Detection of Y-type Dwarfs

Cited by in corpus (43)

• The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU
• Hints for a Turnover at the Snow Line in the Giant Planet Occurrence Rate
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• The International Deep Planet Survey II: The frequency of directly imaged giant exoplanets with stellar mass
• Reconnaissance of the HR 8799 Exosolar System II: Astrometry and Orbital Motion
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• Polarized disk emission from Herbig Ae/Be stars observed using Gemini Planet Imager: HD 144432, HD 150193, HD 163296, and HD 169142
• Performance of the VLT Planet Finder SPHERE I. Photometry and astrometry precision with IRDIS and IFS in laboratory
• A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems
• The SPHERE infrared survey for exoplanets (SHINE)- I Sample definition and target characterization
• The Planetary Accretion Shock: I. Framework for Radiation-hydrodynamical Simulations and First Results
• SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-Mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star
• Planet formation around M dwarfs via disc instability: Fragmentation conditions and protoplanet properties
• Exploring the formation by core accretion and the luminosity evolution of directly imaged planets: The case of HIP 65426 b
• BAFFLES: Bayesian Ages for Field Lower-Mass Stars
• The GAPS Programme with HARPS-N at TNG. XXXVII. A precise density measurement of the young ultra-short period planet TOI-1807 b
• The Young Substellar Companion ROXs 12 B: Near-Infrared Spectrum, System Architecture, and Spin-Orbit Misalignment
• An ALMA Constraint on the GSC 6214-210 B Circum-Substellar Accretion Disk Mass
• BEAST begins: Sample characteristics and survey performance of the B-star Exoplanet Abundance Study
• Searching for Planets in Holey Debris Disks with the Apodizing Phase Plate
• An Explanation of the Very Low Radio Flux of Young Planet-mass Companions
• ISPY-NACO Imaging Survey for Planets around Young stars. The demographics of forming planets embedded in protoplanetary disks
• A Rotation Rate for the Planetary-Mass Companion DH Tau b
• A Wide Planetary Mass Companion Discovered Through the Citizen Science Project Backyard Worlds: Planet 9
• The Exoplanet Simple Orbit Fitting Toolbox (ExoSOFT): An Open-Source Tool for Efficient Fitting of Astrometric and Radial Velocity Data
• Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B
• Migration of accreting planets in radiative discs from dynamical torques
• High Contrast Thermal Infrared Spectroscopy with ALES: The 3-4$\mu$m Spectrum of $\kappa$ Andromedae b
• Non-thermal radio continuum emission from young nearby stars
• The Scorpion Planet Survey: Wide-Orbit Giant Planets Around Young A-type Stars
• A low-mass companion desert among intermediate-mass visual binaries: The scaled-up counterpart to the brown dwarf desert
• The Fundamental Stellar Parameters of FGK Stars in the SEEDS Survey
• HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: III. The population of sub-stellar binary companions
• Indications of M-dwarf Deficits in the Halo and Thick Disk of the Galaxy
• A Simple Depth of Search Metric for Exoplanet Imaging Surveys
• Atmospheric Characterization and Further Orbital Modeling of $\kappa$ And b
• On the survivability of a population of gas giant planets on wide orbits
• VLT/SPHERE survey for exoplanets around young, early-type stars including systems with multi-belt architectures
• GTC/CanariCam deep mid-infrared imaging survey of northern stars within 5 pc
• A Substellar Companion to Pleiades HII 3441
• Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk
• Performance and Early Science with the Subaru Coronagraphic Extreme Adaptive Optics Project
• Developing Linear Dark-Field Control for Exoplanet Direct Imaging in the Laboratory and on Ground-based Telescopes