Epsilon Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

Abstract

The discovery of epsilon Indi Ba, Bb, a binary brown dwarf system very close to the Sun, makes possible a concerted campaign to characterise the physical parameters of two T dwarfs. Recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, but there have been few conclusive tests to date. We therefore aim to characterise these benchmark brown dwarfs to place constraints on such models. We have obtained high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R~5000) spectroscopy of epsilon Indi Ba, Bb with the ESO VLT and present VRIzJHKL'M' broad-band photometry and 0.63--5.1 micron spectroscopy of the individual components. Furthermore, we use deep AO-imaging to place upper limits on the (model-dependent) mass of any further system members. We derive luminosities of log L/L_sun = -4.699+/-0.017 and -5.232+/-0.020 for epsilon Indi Ba, Bb, respectively, and using the dynamical system mass and COND03 evolutionary models predict a system age of 3.7--4.3 Gyr, in excess of previous estimates and recent predictions from observations of these brown dwarfs. Moreover, the effective temperatures of 1352--1385 K and 976--1011 K predicted from the COND03 evolutionary models, for epsilon Indi Ba and Bb respectively, are in disagreement with those derived from the comparison of our data with the BT-Settl atmospheric models where we find effective temperatures of 1300--1340 K and 880--940 K, for epsilon Indi Ba and Bb respectively, with surface gravities of log g=5.25 and 5.50. Finally, we show that spectroscopically determined effective temperatures and surface gravities for ultra-cool dwarfs can lead to underestimated masses even where precise luminosity constraints are available.

27 pages, 30 figures, 9 tables, accepted for publication in Astronomy and Astrophysics

References in corpus (16)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
• Discovery of 11 New T Dwarfs in the Two Micron All-Sky Survey, Including a Possible L/T Transition Binary
• K-H_2 Quasi-molecular absorption detected in the T-dwarf epsilon Indi Ba
• The discovery of an M4+T8.5 binary system
• Exploring the substellar temperature regime down to ~550K
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
• SDSS J080531.84+481233.0: An Unresolved L Dwarf/T Dwarf Binary
• Energy transport, overshoot, and mixing in the atmospheres of M-type main- and pre-main-sequence objects
• Trigonometric parallaxes of ten ultracool subdwarfs
• A high resolution spectral atlas of brown dwarfs
• Dynamical masses for the nearest brown dwarf binary: Epsilon Indi Ba, Bb
• Clouds, Brightening and Multiplicity Across the L Dwarf/T Dwarf Transition

Cited by in corpus (67)

• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
• Stellar and substellar companions of nearby stars from Gaia DR2 - Binarity from proper motion anomaly
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• Individual Dynamical Masses of Ultracool Dwarfs
• Quenching of Carbon Monoxide and Methane in the Atmospheres of Cool Brown Dwarfs and Hot Jupiters
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
• Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations
• Retrieval of atmospheric properties of cloudy L dwarfs
• The 10 parsec sample in the Gaia era
• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• The role of convection, overshoot, and gravity waves for the transport of dust in M dwarf and brown dwarf atmospheres
• Atmospheres from very low-mass stars to extrasolar planets
• Discovery of a Highly Unequal-Mass Binary T Dwarf with Keck Laser Guide Star Adaptive Optics: A Coevality Test of Substellar Theoretical Models and Effective Temperatures
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
• Helios-r2 -- A new Bayesian, open-source retrieval model for brown dwarfs and exoplanet atmospheres
• The properties of the T8.5p dwarf Ross 458C
• Wide, Cool and Ultracool Companions to Nearby Stars from Pan-STARRS1
• AKARI Observations of Brown Dwarfs. III. CO, CO2 and CH4 Fundamental Bands and Physical Parameters
• Impact of a new H/He equation of state on the evolution of massive brown dwarfs. New determination of the hydrogen burning limit
• The planet search programme at the ESO CES and HARPS. IV. The search for Jupiter analogues around solar-like stars
• AKARI Observations of Brown Dwarfs I.: CO and CO_2 Bands in the Near-Infrared Spectra
• Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3
• The Properties of the 500 K Dwarf UGPS J072227.51-054031.2, and a Study of the Far-Red Flux of Cold Brown Dwarfs
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• Three New Cool Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer (WISE) and an Improved Spectrum of the Y0 Dwarf WISE J041022.71+150248.4
• A Dynamical Mass of $70\pm 5$ Jupiter Masses for Gliese 229B, the First T Dwarf
• HIP 38939B: A New Benchmark T Dwarf in the Galactic Plane Discovered with Pan-STARRS1
• Secondary eclipse observations for seven hot-Jupiters from the Anglo-Australian Telescope
• Dynamical Masses of Eps Ind B and C: Two Massive Brown Dwarfs at the Edge of the Stellar-Substellar Boundary
• WISE J072003.20-084651.2B Is A Massive T Dwarf
• COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-Gravity T4 Benchmark around an Old White Dwarf and A Re-Examination of the Surface-Gravity Dependence of the L/T Transition
• The Mass-Luminosity Relation in the L/T Transition: Individual Dynamical Masses for the New J-Band Flux Reversal Binary SDSSJ105213.51+442255.7AB
• The Hyperactive L Dwarf 2MASS J13153094-2649513: Continued Emission and a Brown Dwarf Companion
• Dynamical Mass of the Young Substellar Companion HD 984 B
• A deep WISE search for very late type objects and the discovery of two halo/thick-disk T dwarfs: WISE 0013+0634 and WISE 0833+0052
• Brown Dwarf Binaries from Disintegrating Triple Systems
• Optical and Near-Infrared Spectra of sigma Orionis Isolated Planetary-mass Objects
• An Atmospheric Retrieval of the Brown Dwarf Gliese 229B
• The VAST Survey - IV. A wide brown dwarf companion to the A3V star $\zeta$ Delphini
• Supervised Machine Learning for Intercomparison of Model Grids of Brown Dwarfs: Application to GJ 570D and the Epsilon Indi B Binary System
• High contrast imaging at 10 microns, a search for exoplanets around: Eps Indi A, Eps Eri, Tau Ceti, Sirius A and Sirius B
• The search for disks or planetary objects around directly imaged companions: A candidate around DH Tau B
• Discovery of two L & T binaries with wide separations and peculiar photometric properties
• Search for cool giant exoplanets around young and nearby stars - VLT/NaCo near-infrared phase-coronagraphic and differential imaging
• Orbital and spectral characterization of the benchmark T-type brown dwarf HD 19467B
• Precise Dynamical Masses of Epsilon Indi Ba and Bb: Evidence of Slowed Cooling at the L/T Transition
• Orbital and spectral analysis of the benchmark brown dwarf HD 4747B
• VLT X-shooter spectroscopy of the nearest brown dwarf binary
• Habitable Planets Eclipsing Brown Dwarfs: Strategies for Detection and Characterization
• The first retrieval of a substellar subdwarf: A cloud-free SDSS J125637.13-022452.4
• High-contrast spectroscopy of SCR J1845-6357 B
• Planets Around Low-Mass Stars (PALMS). II. A Low-Mass Companion to the Young M Dwarf GJ 3629 Separated By 0.2"
• Measuring the Initial Mass Function of Low Mass Stars and Brown Dwarfs
• Detectability of satellites around directly imaged exoplanets and brown dwarfs
• Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B
• HST/STIS capability for Love number measurement of WASP-121b
• A search for lithium in metal-poor L dwarfs
• 2MASS J154043.42-510135.7: a new addition to the 5 pc population
• Large-scale changes of the cloud coverage in the $\epsilon$ Indi Ba,Bb system
• One of Everything: The Breakthrough Listen Exotica Catalog
• Characterization of very wide companion candidates to young stars with planets and disks
• SDSS J100711.74+193056.2: A Candidate Common Motion Substellar Companion to the Nearest B-Type Star Regulus
• Benchmark brown dwarfs -- I. A blue M2 + T5 wide binary and a probable young [M4 + M4] + [T7 + T8] hierarchical quadruple
• New constraints on the minimum mass for thermonuclear lithium burning in brown dwarfs