The occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2

Abstract

With the discovery of a planetary system around TRAPPIST-1, there has been a surge of interest in ultracool dwarfs as potential planet hosts. Planetary systems around ultracool dwarfs represent our best chance of characterising temperate rocky-planet atmospheres with JWST. However, TRAPPIST-1 remains the only known system of its kind, and the occurrence rate of planets around ultracool dwarfs is still poorly constrained. We seek to perform a complete transit search on the ultracool dwarfs observed by NASA's K2 mission to constrain the occurrence rate of planets around these stars. We filter and characterise the sample of ultracool dwarfs observed by K2, by fitting their spectral energy distributions and using parallaxes from Gaia. We build an automatic pipeline to perform photometry, detrend the lightcurves, and search for transits. Using extensive injection-recovery tests of our pipeline, we compute the detection sensitivity of our search, and thus the completeness of our sample. We infer the planetary occurrence rates within a hierarchical Bayesian model (HBM) to treat uncertain planetary parameters. With the occurrence rate parametrised by a step-wise function, we show a convenient way to directly marginalise over the second level of our HBM (the planet parameters). Our method is applicable generally and can greatly speed up inference with larger catalogues of detected planets. We detect one planet in our sample of 702 ultracool dwarfs: a previously-validated mini-Neptune. We thus infer a mini-Neptune (2 - 4Re) occurrence rate of η = 0.20+0.16-0.11 within orbital periods of 1 - 20 days. For super-Earths (1 - 2Re) and ice/gas giants (4 - 6Re) within 1 - 20 days, we place 95% credible intervals of η < 1.14 and η < 0.29, respectively. If TRAPPIST-1-like systems were ubiquitous, we would have had a 96% chance of finding at least one.

arXiv commentAccepted in A&A on 29/04/2020, 13 pages, 6 figures

References in corpus (68)

• emcee: The MCMC Hammer
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• Analytic Lightcurves for Planetary Transit Searches
• The K2 Mission: Characterization and Early results
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• The false positive rate of Kepler and the occurrence of planets
• batman: BAsic Transit Model cAlculatioN in Python
• 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
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• Giant Planet Occurrence in the Stellar Mass-Metallicity Plane
• Temperate Earth-sized planets transiting a nearby ultracool dwarf star
• Overview of the Kepler Science Processing Pipeline
• The Occurrence Rate of Small Planets around Small Stars
• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• Stellar Diameters and Temperatures II. Main Sequence K & M Stars
• Design Considerations for a Ground-based Transit Search for Habitable Planets Orbiting M dwarfs
• A seven-planet resonant chain in TRAPPIST-1
• The Fifteenth Data Release of the Sloan Digital Sky Surveys: First Release of MaNGA Derived Quantities, Data Visualization Tools and Stellar Library
• The nature of the TRAPPIST-1 exoplanets
• A stellar-mass-dependent drop in planet occurrence rates
• The K2 Ecliptic Plane Input Catalog (EPIC) and Stellar Classifications of 138,600 Targets in Campaigns 1-8
• Exoplanet population inference and the abundance of Earth analogs from noisy, incomplete catalogs
• A revised estimate of the occurrence rate of terrestrial planets in the habitable zones around kepler m-dwarfs
• Probabilistic Mass-Radius Relationship for Sub-Neptune-Sized Planets
• A Plateau in the Planet Population Below Twice the Size of Earth
• The Exoplanet Population Observation Simulator. I - The Inner Edges of Planetary Systems
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• Planetary Candidates from the First Year of the K2 Mission
• An Increase in the Mass of Planetary Systems around Lower-Mass Stars
• The Exoplanet Census: A General Method, Applied to Kepler
• Inferring the eccentricity distribution
• Occurrence Rates of Planets orbiting FGK Stars: Combining Kepler DR25, Gaia DR2 and Bayesian Inference
• They are Small Worlds After All: Revised Properties of Kepler M Dwarf Stars and their Planets
• Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type
• The Radius Distribution of Planets Around Cool Stars
• A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars
• 275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0-10
• Zodiacal Exoplanets In Time (ZEIT) I: A Neptune-sized planet orbiting an M4.5 dwarf in the Hyades Star Cluster
• Biosignature Gases in H2-Dominated Atmospheres on Rocky Exoplanets
• The Kepler Dichotomy among the M Dwarfs: Half of Systems Contain Five or More Coplanar Planets
• Gaia Data Release 2. Cross-match with external catalogues - Algorithms and results
• They might be giants: luminosity class, planet frequency, and planet-metallicity relation of the coolest Kepler target stars
• Fast Rise of "Neptune-Size" Planets ($4-8R_{\mathrm{Earth}}$) from $P\sim 10$ to $\sim 250$ days -- Statistics of Kepler Planet Candidates Up to $\sim 0.75\mathrm{AU}$
• Characterizing the Cool KOIs IV: Kepler-32 as a prototype for the formation of compact planetary systems throughout the Galaxy
• Super-Earth masses sculpted by pebble isolation around stars of different masses
• Kepler-445, Kepler-446 and the Occurrence of Compact Multiples Orbiting Mid-M Dwarf Stars
• Occurrence Rates of Planets Orbiting M Stars: Applying ABC to Kepler DR25, Gaia DR2, and 2MASS Data
• New low-mass eclipsing binary systems in Praesepe discovered by K2
• Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars II: Planetary Systems Observed During Campaigns 1-7
• Formation and composition of planets around very low mass stars
• Constraints on Planet Occurrence around Nearby Mid-to-Late M Dwarfs from the MEarth Project
• Detection of Hundreds of New Planet Candidates and Eclipsing Binaries in K2 Campaigns 0-8
• New Pleiades Eclipsing Binaries and a Hyades Transiting System Identified by K2
• Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars I: Classifying Low-mass Host Stars Observed During Campaigns 1-7
• First limits on the occurrence rate of short-period planets orbiting brown dwarfs
• Sensitive Probing of Exoplanetary Oxygen via Mid Infrared Collisional Absorption
• A Universal Break in the Planet-to-Star Mass-Ratio Function of Kepler MKG stars
• An Understanding of the Shoulder of Giants: Jovian Planets around Late K Dwarf Stars and the Trend with Stellar Mass
• Pan-Planets: Searching for hot Jupiters around cool dwarfs
• Upper Limits on Planet Occurrence around Ultracool Dwarfs with K2
• Probing TRAPPIST-1-like systems with K2

Cited by in corpus (13)

• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• The New Generation Planetary Population Synthesis (NGPPS). II. Planetary population of solar-like stars and overview of statistical results
• Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O${}_2$ Levels in Nearby Transiting Habitable Zone Exoplanets
• The dynamics of the TRAPPIST-1 system in the context of its formation
• The CARMENES search for exoplanets around M dwarfs, Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby, very low-mass star
• An Increase in Small-planet Occurrence with Metallicity for Late-type Dwarf Stars in the Kepler Field and Its Implications for Planet Formation
• Assessing $TESS$'s Yield of Rocky Planets Around Nearby M Dwarfs
• Predicting the Yield of Small Transiting Exoplanets around Mid-M and Ultra-Cool Dwarfs in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey
• EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc
• The Perkins INfrared Exosatellite Survey (PINES) II. Transit Candidates and Implications for Planet Occurrence around L and T Dwarfs
• Scaling K2 VIII: Short-Period Sub-Neptune Occurrence Rates Peak Around Early-Type M Dwarfs
• A false positive transit candidate for EPIC 211101996 from K2 and TESS data identified as background eclipsing binary Gaia DR3 66767847894609792
• The Perkins INfrared Exosatellite Survey (PINES) I. Survey Overview, Reduction Pipeline, and Early Results