Three statistically validated K2 transiting warm Jupiter exoplanets confirmed as low-mass stars

Abstract

We have identified three K2 transiting star-planet systems, K2-51 (EPIC 202900527), K2-67 (EPIC 206155547), and K2-76 (EPIC 206432863), as stellar binaries with low-mass stellar secondaries. The three systems were statistically validated as transiting planets, and through measuring their orbits by radial velocity monitoring we have derived the companion masses to be $0.1459_{-0.0032}^{+0.0029}$ $M_{Sun}$ (EPIC 202900527 B), $0.1612_{-0.0067}^{+0.0072}$ $M_{Sun}$ (EPIC 206155547 B), and $0.0942\pm 0.0019$ $M_{Sun}$ (EPIC 206432863 B). Therefore they are not planets but small stars, part of the small sample of low-mass stars with measured radius and mass. The three systems are at an orbital period range of $12-24$ days, and the secondaries have a radius within $0.9-1.9$ $R_J$, not inconsistent with the properties of warm Jupiter planets. These systems illustrate some of the existing challenges in the statistical validation approach. We point out a few possible origins for the initial misclassification of these objects, including poor characterization of the host star, the difficulty in detecting a secondary eclipse in systems on an eccentric orbit, and the difficulty in distinguishing between the smallest stars and gas giant planets as the two populations have indistinguishable radius distributions. Our work emphasizes the need for obtaining medium-precision radial velocity measurements to distinguish between companions that are small stars, brown dwarfs, and gas giant planets.

Accepted to ApJ Letters

References in corpus (39)

• emcee: The MCMC Hammer
• Analytic Lightcurves for Planetary Transit Searches
• The Dartmouth Stellar Evolution Database
• The K2 Mission: Characterization and Early results
• Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The PLATO 2.0 Mission
• The false positive rate of Kepler and the occurrence of planets
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Radial Velocities for 889 Late-type Stars
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• The Transiting Exoplanet Survey Satellite: Simulations of planet detections and astrophysical false positives
• False positive probabilties for all Kepler Objects of Interest: 1284 newly validated planets and 428 likely false positives
• HAT-P-16b: A 4 Mj Planet Transiting A Bright Star On An Eccentric Orbit
• Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2
• The California-Kepler Survey. I. High Resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets
• An Efficient Automated Validation Procedure for Exoplanet Transit Candidates
• Modeling Kepler transit light curves as false positives: Rejection of blend scenarios for Kepler-9, and validation of Kepler-9d, a super-Earth-size planet in a multiple system
• Planetary Candidates Observed by Kepler. VII. The First Fully Uniform Catalog Based on The Entire 48 Month Dataset (Q1-Q17 DR24)
• Planetary Candidates from the First Year of the K2 Mission
• 197 Candidates and 104 Validated Planets in K2's First Five Fields
• Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
• The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations
• The Dependence of Brown Dwarf Radii on Atmospheric Metallicity and Clouds: Theory and Comparison with Observations
• Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone
• The EBLM Project I-Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the Brown Dwarf limit
• The NASA-UC Eta-Earth Program: I. A Super-Earth Orbiting HD 7924
• A planet-sized transiting star around OGLE-TR-122 - Accurate mass and radius near the Hydrogen-burning limit
• Fundamental properties of lower main-sequence stars
• SOPHIE velocimetry of Kepler transit candidates IX. KOI-415 b: a long-period, eccentric transiting brown dwarf to an evolved Sun
• Radial velocity monitoring of Kepler heartbeat stars
• The Mass-Radius Relationship for Very Low Mass Stars: Four New Discoveries from the HATSouth Survey
• SOPHIE velocimetry of Kepler transit candidates. VIII. KOI-205 b: a brown-dwarf companion to a K-type dwarf
• EPIC201702477b: A Long Period Transiting Brown Dwarf from K2
• SOPHIE velocimetry of Kepler transit candidates. XIII. KOI-189 B and KOI-686 B: two very low-mass stars in long-period orbits
• The EBLM project III. A Saturn-size low-mass star at the hydrogen-burning limit
• KIC 1571511B: A Benchmark Low-Mass Star In An Eclipsing Binary System In The Kepler Field
• CoRoT LRa02_E2_0121: Neptune-size planet candidate turns into a hierarchical triple system with a giant primary

Cited by in corpus (23)

• The scatter of the M dwarf mass-radius relationship
• KELT-20b: A giant planet with a period of P~ 3.5 days transiting the V~ 7.6 early A star HD 185603
• Zodiacal Exoplanets in Time (ZEIT) VIII: A Two Planet System in Praesepe from K2 Campaign 16
• 60 Validated Planets from K2 Campaigns 5-8
• 44 Validated Planets from K2 Campaign 10
• Diffuser-Assisted Infrared Transit Photometry for Four Dynamically Interacting \textit{Kepler} Systems
• Discovery and Vetting of Exoplanets I: Benchmarking K2 Vetting Tools
• Populating the brown dwarf and stellar boundary: Five stars with transiting companions near the hydrogen-burning mass limit
• Automatic vetting of planet candidates from ground based surveys: Machine learning with NGTS
• 37 New Validated Planets in Overlapping K2 Campaigns
• The nature of the giant exomoon candidate Kepler-1625 b-i
• Validation of small Kepler transiting planet candidates in or near the habitable zone
• Ondr}ejov echelle spectrograph, ground based support facility for exoplanet missions
• The K2-OjOS Project: New and revisited planets and candidates in K2 campaigns 5, 16, & 18
• Validation of TESS exoplanet candidates orbiting solar analogues in the all-sky PLATO input catalogue
• Spitzer transit follow-up of planet candidates from the K2 mission
• A 38 Million Year Old Neptune-Sized Planet in the Kepler Field
• TOI 694 b and TIC 220568520 b: Two Low-Mass Companions Near the Hydrogen Burning Mass Limit Orbiting Sun-like Stars
• Pterodactyls: A Tool to Uniformly Search and Vet for Young Transiting Planets In TESS Primary Mission Photometry
• Planetary candidates transiting cool dwarf stars from Campaigns 12 to 15 of K2
• Revisiting Kepler Transiting Systems: Unvetting Planets and Constraining Relationships among Harmonics in Phase Curves
• TOI-1438: A rare system with two short-period sub-Neptunes and a tentative long-period Jupiter-like planet orbiting a K0V star
• Evidence of Radius Inflation Based on 50 Transiting Brown Dwarfs and Low-mass Stellar Companions