A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late-T Dwarfs

Abstract

The spectra of brown dwarfs are key to exploring the chemistry and physics that take place in their atmospheres. Late-T dwarf spectra are particularly diagnostic due to their relatively cloud-free atmospheres and deep molecular bands. With the use of powerful atmospheric retrieval tools applied to the spectra of these objects, direct constraints on molecular/atomic abundances, gravity, and vertical thermal profiles can be obtained enabling a broad exploration of the chemical/physical mechanisms operating in their atmospheres. We present a uniform retrieval analysis on low-resolution IRTF SpeX near-IR spectra of a sample of 50 T dwarfs, including new observations as part of a recent volume-limited survey. This analysis more than quadruples the sample of T dwarfs with retrieved temperature profiles and abundances (H${}_2$O, CH${}_4$, NH${}_3$, K and subsequent C/O and metallicities). We are generally able to constrain effective temperatures to within 50K, volume mixing ratios for major species to within 0.25dex, atmospheric metallicities [M/H] to within 0.2, and C/O ratios to within 0.2. We compare our retrieved constraints on the thermal structure, chemistry, and gravities of these objects with predictions from self-consistent radiative-convective equilibrium models and find, in general though with substantial scatter, consistency with solar composition chemistry and thermal profiles of the neighboring stellar FGK population. Objects with notable discrepancies between the two modeling techniques and potential mechanisms for their differences, be they related to modeling approach or physically motivated, are discussed more thoroughly in the text.

arXiv comment21 pages, 11 figures

References in corpus (67)

• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945
• The effects of snowlines on C/O in planetary atmospheres
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• Chemical Equilibrium Abundances in Brown Dwarf and Extrasolar Giant Planet Atmospheres
• L' and M' Photometry of Ultracool Dwarfs
• Neglected Clouds in T and Y Dwarf Atmospheres
• The Formation Mechanism of Brown Dwarfs
• The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B
• A Framework for Characterizing the Atmospheres of Low-Mass Low-Density Transiting Planets
• H- Opacity and Water Dissociation in the Dayside Atmosphere of the Very Hot Gas Giant WASP-18 b
• Stellar Abundances in the Solar Neighborhood: The Hypatia Catalog
• Towards Chemical Constraints on Hot Jupiter Migration
• The Brown Dwarf Kinematics Project (BDKP). III. Parallaxes for 70 Ultracool Dwarfs
• Infrared Parallaxes for Methane T dwarfs
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• Individual Dynamical Masses of Ultracool Dwarfs
• Water Clouds in Y Dwarfs and Exoplanets
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• Mid-Infrared Photometry of Cold Brown Dwarfs: Diversity in Age, Mass and Metallicity
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Theory for the Secondary Eclipse Fluxes, Spectra, Atmospheres, and Light Curves of Transiting Extrasolar Giant Planets
• The minimum mass for star formation, and the origin of binary brown dwarfs
• The Spectrum of the Brown Dwarf Gliese 229B
• Retrieval of atmospheric properties of cloudy L dwarfs
• Constructing A Flexible Likelihood Function For Spectroscopic Inference
• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• Metallicity Gradient of a Lensed Face-on Spiral Galaxy at Redshift 1.49
• Photometry and Proper Motions of M, L, and T Dwarfs from the Pan-STARRS1 3$\pi$ Survey
• Clouds in the Coldest Brown Dwarfs: FIRE Spectroscopy of Ross 458C
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs II: Properties of 11 T-dwarfs
• Physical parameters of two very cool T dwarfs
• Disk evolution, element abundances and cloud properties of young gas giant planets
• Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• Water, High-Altitude Condensates, and Possible Methane Depletion in the Atmosphere of the Warm Super-Neptune WASP-107b
• A HST/WFC3 Thermal Emission Spectrum of the Hot Jupiter HAT-P-7b
• Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs
• Atmospheres of Brown Dwarfs
• The properties of the T8.5p dwarf Ross 458C
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• AKARI Observations of Brown Dwarfs. III. CO, CO2 and CH4 Fundamental Bands and Physical Parameters
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• A Uniform Retrieval Analysis of Ultracool Dwarfs. III. Properties of Y-Dwarfs
• Spectroscopy across the brown dwarf/planetary mass boundary - I. Near-infrared JHK spectra
• The Properties of the 500 K Dwarf UGPS J072227.51-054031.2, and a Study of the Far-Red Flux of Cold Brown Dwarfs
• Spectroscopic Detection of Carbon Monoxide in Two Late-type T Dwarfs
• Ground- and Space-based Detection of the Thermal Emission Spectrum of the Transiting Hot Jupiter KELT-2Ab
• Methane and Ammonia in the near-infrared spectra of late T dwarfs
• New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• Retrieval of SDSS J1416+1348AB
• An Approach for Retrieving Temperatures and Abundances in Brown Dwarf Atmospheres
• The Influence of H2O Pressure Broadening in High Metallicity Exoplanet Atmospheres
• Uniform Forward-Modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking
• An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Sub-Solar Water Abundance
• The TESS Phase Curve of KELT-1b Suggests a High Dayside Albedo
• The Sonora Brown Dwarf Atmosphere and Evolution Models I. Model Description and Application to Cloudless Atmospheres in Rainout Chemical Equilibrium