Uncovering the ultimate planet impostor. An eclipsing brown dwarf in a hierarchical triple with two evolved stars

Abstract

Exoplanet searches through space-based photometric time series have shown to be very efficient in recent years. However, follow-up efforts on the detected planet candidates have been demonstrated to be critical to uncover the true nature of the transiting objects. In this paper we show a detailed analysis of one of those false positives hidden as planetary signals. In this case, the candidate KOI-3886.01 showed clear evidence of a planetary nature from various techniques. Indeed, the properties of the fake planet set it among the most interesting and promising for the study of planetary evolution as the star leaves the main sequence. To unveil the true nature of this system, we present a complete set of observational techniques including high-spatial resolution imaging, high-precision photometric time series (showing eclipses, phase curve variations and asteroseismology signals), high-resolution spectroscopy and derived radial velocities, to unveil the true nature of this planet candidate. We find that KOI-3886.01 is an interesting false positive case: a hierarchical triple system composed by a $\sim$K2III giant star (KOI-3886A) accompanied by a close-in eclipsing binary formed by a subgiant $\sim$G4IV star (KOI-3886B) and a brown dwarf (KOI-3886C). In particular, KOI-3886C is one of the most irradiated brown dwarfs known to date, showing the largest radius in this substellar regime. It is also the first eclipsing brown dwarf known around an evolved star. In this paper we highlight the relevance of complete sets of follow-up observations to extrasolar planets detected by the transit technique using large-pixel photometers such as Kepler and TESS, and in the future, PLATO. In particular, multi-color high-spatial resolution imaging was the first hint toward ruling out the planet scenario in this system.

arXiv commentAccepted for publication in A&A, 21 pages, 18 figures, 5 tables (language corrected version)

References in corpus (90)

• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Sloan Digital Sky Survey: Technical Summary
• The chemical composition of the Sun
• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• 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
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Astrophysics Source Code Library
• Gaia Early Data Release 3: The astrometric solution
• batman: BAsic Transit Model cAlculatioN in Python
• Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
• Long-Term Stability of Planets in Binary Systems
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• Spectral Irradiance Calibration in the Infrared. XIV: the Absolute Calibration of 2MASS
• GYRE: An open-source stellar oscillation code based on a new Magnus Multiple Shooting Scheme
• HERMES: a high-resolution fibre-fed spectrograph for the Mercator telescope
• Juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems
• A new code for automatic determination of equivalent widths: Automatic Routine for line Equivalent widths in stellar Spectra (ARES)
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets
• The Orbital Evolution of Gas Giant Planets around Giant Stars
• Preparation of Kepler lightcurves for asteroseismic analyses
• Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• The CORALIE survey for southern extra-solar planets IX. A 1.3-day period brown dwarf disguised as a planet
• Asteroseismology of 16000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii
• The underlying physical meaning of the ${\nu }_{\max }-{\nu }_{\mathrm{c}}$ relation
• ARES v2 - new features and improved performance
• Hot Jupiters and Cool Stars
• A sub-Mercury-sized exoplanet
• Deriving precise parameters for cool solar-type stars. Optimizing the iron line list
• ELLC - a fast, flexible light curve model for detached eclipsing binary stars and transiting exoplanets
• Robotic Laser-Adaptive-Optics Imaging of 715 Kepler Exoplanet Candidates using Robo-AO
• An ultra-short period rocky super-Earth with a secondary eclipse and a Neptune-like companion around K2-141
• High-resolution imaging of $Kepler$ planet host candidates. A comprehensive comparison of different techniques
• Impact on asteroseismic analyses of regular gaps in Kepler data
• DIAMONDS: a new Bayesian Nested Sampling tool. Application to Peak Bagging of solar-like oscillations
• Kepler-91b: a planet at the end of its life. Planet and giant host star properties via light-curve variations
• Multiplicity in transiting planet host stars. A Lucky Imaging study of Kepler candidates
• Age Determination in Upper Scorpius with Eclipsing Binaries
• New low-mass eclipsing binary systems in Praesepe discovered by K2
• On the use of marginal posteriors in marginal likelihood estimation via importance-sampling
• Constraining Orbital Parameters Through Planetary Transit Monitoring
• On using the CMD morphology of M67 to test solar abundances
• ARES+MOOG - a practical overview of an EW method to derive stellar parameters
• Revised Filter Profiles and Zero Points for Broadband Photometry
• Deep Learning Classification in Asteroseismology
• Star Hoppers: Planet Instability and Capture in Evolving Binary Systems
• Kepler KOI-13.01 - Detection of beaming and ellipsoidal modulations pointing to a massive hot Jupiter
• Robo-AO Kepler Planetary Candidate Survey III: Adaptive Optics Imaging of 1629 Kepler Exoplanet Candidate Host Stars
• A New Method for the Asteroseismic Determination of the Evolutionary State of Red-Giant Stars
• New Pleiades Eclipsing Binaries and a Hyades Transiting System Identified by K2
• CAFE: Calar Alto Fiber-fed Echelle spectrograph
• MuSCAT2 multicolour validation of TESS candidates: an ultra-short-period substellar object around an M dwarf
• NGTS-7Ab: An ultra-short period brown dwarf transiting a tidally-locked and active M dwarf
• Two intermediate-mass transiting brown dwarfs from the TESS mission
• An irradiated brown-dwarf companion to an accreting white dwarf
• TESS Asteroseismology of the known red-giant host stars HD 212771 and HD 203949
• Asteroseismology of 36 Kepler subgiants -- II: Determining ages from detailed modelling
• TOI-811b and TOI-852b: New transiting brown dwarfs with similar masses and very different radii and ages from the TESS mission
• Red Giant evolution and specific problems
• Amplitude and lifetime of radial modes in red giant star spectra observed by Kepler
• TOI-503: The first known brown dwarf-Am star binary from the TESS mission
• AstraLux - the Calar Alto 2.2-m telescope Lucky Imaging camera
• The Radial Velocity Signature of Tides Raised in Stars Hosting Exoplanets
• New substellar discoveries from Kepler and K2: Is there a brown dwarf desert?
• Weighing in on the masses of retired A stars with asteroseismology: K2 observations of the exoplanet-host star HD 212771
• An eclipsing double-line spectroscopic binary at the stellar/substellar boundary in the Upper Scorpius OB association
• The MgI line: a new probe of the atmospheres of evaporating exoplanets
• Fast and Automated Peak Bagging with DIAMONDS (FAMED)
• The cluster ages experiment (CASE). VII. Analysis of two eclipsing binaries in the globular cluster NGC 6362
• ESPRESSO Mass determination of TOI-263b: An extreme inhabitant of the brown dwarf desert
• Deep GALEX UV Survey of the Kepler Field I: Point Source Catalog
• Supervised Learning Detection of Sixty Non-Transiting Hot Jupiter Candidates
• Visual Orbits of Spectroscopic Binaries with the CHARA Array. I. HD 224355
• Close-in planets around giant stars. Lack of hot-Jupiters and prevalence of multi-planetary systems
• CAFE2: an upgrade to the CAFE high-resolution spectrograph. Commissioning results and new public pipeline
• Properties of the Hyades, the eclipsing binary HD27130, and the oscillating red giant $\epsilon$ Tau
• A data base of synthetic photometry in the GALEX ultraviolet bands for the stellar sources observed with the International Ultraviolet Explorer
• The triple system HIP96515: a low-mass eclipsing binary with a DB white dwarf companion
• Visual Orbits of Spectroscopic Binaries with the CHARA Array. II. The eclipsing binary HD 185912
• Visual Orbits of Spectroscopic Binaries with the CHARA Array. III. HD 8374 and HD 24546
• KIC 2568888: To be or not to be a binary
• Follow-up of non-transiting planets detected by Kepler. Confirmation of three hot-Jupiters and validation of three other planets

Cited by in corpus (4)

• Revisiting the Red-giant Branch Hosts KOI-3886 and $\iota$ Draconis. Detailed Asteroseismic Modeling and Consolidated Stellar Parameters
• The AstraLux-TESS high-spatial resolution imaging survey. Search for stellar companions of 215 planet candidates from TESS
• Gaia0007-1605: an old triple system with an inner brown dwarf-white dwarf binary and an outer white dwarf companion
• The role of triple evolution in the formation of LISA double white dwarfs