Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B

Abstract

Interpreting the spectra of brown dwarfs is key to determining the fundamental physical and chemical processes occurring in their atmospheres. Powerful Bayesian atmospheric retrieval tools have recently been applied to both exoplanet and brown dwarf spectra to tease out the thermal structures and molecular abundances to understand those processes. In this manuscript we develop a significantly upgraded retrieval method and apply it to the SpeX spectral library data of two benchmark late T-dwarfs, Gl570D and HD3651B, to establish the validity of our upgraded forward model parameterization and Bayesian estimator. Our retrieved metallicities, gravities, and effective temperature are consistent with the metallicity and presumed ages of the systems. We add the carbon-to-oxygen ratio as a new dimension to benchmark systems and find good agreement between carbon-to-oxygens ratio derived in the brown dwarfs and the host stars. Furthermore, we have for the first time unambiguously determined the presence of ammonia in the low-resolution spectra of these two late T-dwarfs. We also show that the retrieved results are not significantly impacted by the possible presence of clouds, though some quantities are significantly impacted by uncertainties in photometry. This investigation represents a watershed study in establishing the utility of atmospheric retrieval approaches on brown dwarf spectra.

submitted to Apj, addressed first round of minor revisions

References in corpus (25)

• Bayes in the sky: Bayesian inference and model selection in cosmology
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• The NASA-UC-UH Eta-Earth Program: IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth
• Stellar Abundances in the Solar Neighborhood: The Hypatia Catalog
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• Stellar Parameters and Metallicities of Stars Hosting Jovian and Neptunian Mass Planets: A Possible Dependence of Planetary Mass on Metallicity
• Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• Carbon and oxygen abundances in stellar populations
• The spectrum of hot methane in astronomical objects using a comprehensive computed line list
• Finding benchmark brown dwarfs to probe the IMF as a function of time
• Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
• HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star
• C/O Ratios of Stars with Transiting Hot Jupiter Exoplanets
• Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry
• The Physical Properties of HD 3651B: An Extrasolar Nemesis?
• Abundance Differences Between Exoplanet Binary Host Stars XO-2N and XO-2S -- Dependence on Stellar Parameters
• Methane and Ammonia in the near-infrared spectra of late T dwarfs
• The non-LTE line formation of neutral carbon in late-type stars
• An Approach for Retrieving Temperatures and Abundances in Brown Dwarf Atmospheres

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