Panchromatic characterization of the Y0 brown dwarf WISEP J173835.52+273258.9 using JWST/MIRI

Abstract

Cold brown dwarf atmospheres are good training grounds for analyzing temperate giant planets. WISEP J173835.52+273258.9 (WISE 1738) is an isolated Y0 brown dwarf with a temperature between 350-400 K, at the T-Y transition. While its near-infrared spectrum has been studied, bulk properties and chemistry remain uncertain. We analyze new JWST MIRI medium-resolution spectra (5-18 micron), combined with near-infrared spectra (0.98-2.2 micron) from HST/WFC3 and Gemini/GNIRS, to better constrain WISE 1738's atmosphere and physical parameters. We use Neural Posterior Estimation (NPE) with a cloud-free petitRADTRANS model and evaluate results using posterior checks, coverage, and L-C2ST diagnostics. Our retrieval confirms previous constraints on H2O, CH4, and NH3, and for the first time constrains CO, CO2, and 15NH3. We find evidence of disequilibrium chemistry through CO and CO2 abundances not expected under equilibrium. Estimated properties are temperature 402 (+12,-9) K, log g 4.43 (+0.26,-0.34) cm/s2, mass 13 (+11,-7) M_Jup, radius 1.14 (+0.03,-0.03) R_Jup, and bolometric luminosity -6.52 (+0.05,-0.04) log L/L_sun. Evolutionary models suggest an age between 1 and 4 Gyr, consistent with a 6-hour rotation. We place an upper bound on 15NH3, implying a 3-sigma lower limit on the 14N/15N ratio of 275. We also derive a C/O ratio of 1.35 (+0.39,-0.31) and metallicity of 0.34 (+0.12,-0.11), without accounting for oxygen sequestration.

References in corpus (51)

• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• A Temperature and Abundance Retrieval Method for Exoplanet Atmospheres
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• 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 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)
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• Stellar Abundances in the Solar Neighborhood: The Hypatia Catalog
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars II. Sulfur and Phosphorus
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• The Mid-Infrared Instrument for JWST, II: Design and Build
• JWST MIRI flight performance: The Medium-Resolution Spectrometer
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Observing transiting planets with JWST -- Prime targets and their synthetic spectral observations
• Water Clouds in Y Dwarfs and Exoplanets
• Exoplanet Reflected Light Spectroscopy with PICASO
• Quenching of Carbon Monoxide and Methane in the Atmospheres of Cool Brown Dwarfs and Hot Jupiters
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Molecular Abundances in the Atmosphere of the T Dwarf Gl 229B
• New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown dwarfs
• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• PICASO 3.0: A One-Dimensional Climate Model for Giant Planets and Brown Dwarfs
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs II: Properties of 11 T-dwarfs
• Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• The Atomic and Molecular Content of Disks Around Very Low-mass Stars and Brown Dwarfs
• The Sonora Substellar Atmosphere Models. IV. Elf Owl: Atmospheric Mixing and Chemical Disequilibrium with Varying Metallicity and C/O Ratios
• WISE Y Dwarfs As Probes of the Brown Dwarf-Exoplanet Connection
• Phase Functions and Light Curves of Wide Separation Extrasolar Giant Planets
• 3.6-7.9 um Photometry of L and T Dwarfs and the Prevalence of Vertical Mixing in their Atmospheres
• Optical Albedo Theory of Strongly-Irradiated Giant Planets: The Case of HD 209458b
• The Y-Type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry and Near-Infrared Spectroscopy
• Chemistry of Low Mass Substellar Objects
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• A Uniform Retrieval Analysis of Ultracool Dwarfs. III. Properties of Y-Dwarfs
• Abundant hydrocarbons in the disk around a very-low-mass star
• An L Band Spectrum of the Coldest Brown Dwarf
• Probing the Extent of Vertical Mixing in Brown Dwarf Atmospheres with Disequilibrium Chemistry
• Self-consistent Models of Y Dwarf Atmospheres with Water Clouds and Disequilibrium Chemistry
• Neural posterior estimation for exoplanetary atmospheric retrieval
• Observed Variability at 1um and 4um in the Y0 Brown Dwarf WISEP J173835.52+273258.9
• 15NH3 in the atmosphere of a cool brown dwarf
• Y dwarf Trigonometric Parallaxes from the Spitzer Space Telescope
• Near-Infrared Spectroscopy of the Y0 WISEP J173835.52+273258.9 and the Y1 WISE J035000.32-565830.2: the Importance of Non-Equilibrium Chemistry
• MINDS: The very low-mass star and brown dwarf sample. Detections and trends in the inner disk gas
• Towards Robust Atmospheric Retrieval on Cloudy L Dwarfs: The Impact of Thermal and Abundance Profile Assumptions
• Water depletion and 15NH3 in the atmosphere of the coldest brown dwarf observed with JWST/MIRI