Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs

Abstract

Cold brown dwarfs are excellent analogs of widely separated, gas giant exoplanets, and provide insight into the potential atmospheric chemistry and physics we may encounter in objects discovered by future direct imaging surveys. We present a low resolution R $\sim$ 300 $M$-band spectroscopic sequence of seven brown dwarfs with effective temperatures between 750 K and 250 K along with Jupiter. These spectra reveal disequilibrium abundances of carbon monoxide (CO) produced by atmospheric quenching. We use the eddy diffusion coefficient (K${}_{zz}$) to estimate the strength of vertical mixing in each object. The K${}_{zz}$ values of cooler gaseous objects are close to their theoretical maximum and warmer objects show weaker mixing, likely due to less efficient convective mixing in primarily radiative layers. The CO-derived K${}_{zz}$ values imply that disequilibrium phosphine (PH${}_3$) should be easily observable in all of the brown dwarfs, but none as yet show any evidence for PH${}_3$ absorption. We find that ammonia is relatively insensitive to atmospheric quenching at these effective temperatures. We are able to improve the fit to WISE 0855's $M$-band spectrum by including both CO and water clouds in the atmospheric model.

arXiv commentAccepted to the Astronomical Journal. 24 Pages, 16 Figures, 4 Tables. take care

References in corpus (54)

• Precipitating Condensation Clouds in Substellar Atmospheres
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: the Effects of Temperature, Clouds, and Gravity
• A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
• L' and M' Photometry of Ultracool Dwarfs
• The Mass-Metallicity Relation for Giant Planets
• The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)
• The Discovery of Y Dwarfs Using Data from the Wide-field Infrared Survey Explorer (WISE)
• Imaging Extrasolar Giant Planets
• Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs
• Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars II. Sulfur and Phosphorus
• Population Properties of Brown Dwarf Analogs to Exoplanets
• Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra
• Discovery of a Brown Dwarf Companion to Gliese 570ABC: A 2MASS T Dwarf Significantly Cooler than Gliese 229B
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun
• Spitzer/IRAC Photometry of M, L, and T Dwarfs
• Water Clouds in Y Dwarfs and Exoplanets
• Quenching of Carbon Monoxide and Methane in the Atmospheres of Cool Brown Dwarfs and Hot Jupiters
• A new equation of state for dense hydrogen-helium mixtures
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• The Spectrum of the Brown Dwarf Gliese 229B
• The discovery of a very cool, very nearby brown dwarf in the Galactic plane
• The Young Planet-mass Object 2M1207b: a cool, cloudy, and methane-poor atmosphere
• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• Infrared Observations and Modeling of one of the Coolest T Dwarfs, Gl 570D
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs II: Properties of 11 T-dwarfs
• Physical parameters of two very cool T dwarfs
• Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• The Deep Water Abundance on Jupiter: New Constraints from Thermochemical Kinetics and Diffusion Modeling
• WISE Y Dwarfs As Probes of the Brown Dwarf-Exoplanet Connection
• The Y-Type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry and Near-Infrared Spectroscopy
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• A Comparison of Near-Infrared Photometry and Spectra for Y Dwarfs with a New Generation of Cool Cloudy Models
• AKARI Observations of Brown Dwarfs. III. CO, CO2 and CH4 Fundamental Bands and Physical Parameters
• A Uniform Retrieval Analysis of Ultracool Dwarfs. III. Properties of Y-Dwarfs
• 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
• An L Band Spectrum of the Coldest Brown Dwarf
• The First Spectrum of the Coldest Brown Dwarf
• Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
• Indications of Water Clouds in the Coldest Known Brown Dwarf
• The Spectral Energy Distribution of the Coldest Known Brown Dwarf
• Photometric Monitoring of the Coldest Known Brown Dwarf with the Spitzer Space Telescope
• Methane in Analogs of Young Directly Imaged Exoplanets
• NEOWISE-R Observation of the Coolest Known Brown Dwarf
• Properties of the T8.5 Dwarf Wolf 940 B
• The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5
• 3.8um Imaging of 400-600K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB
• Modeling synthetic spectra for transiting extrasolar giant planets: detectability of H${}_2$S and PH${}_3$ with JWST

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