Physical Parameters and Properties of 20 Cold Brown Dwarfs in JWST

Abstract

We present a comprehensive analysis of 20 T and Y dwarfs using spectroscopy from the NIRSpec CLEAR/PRISM and MIRI LRS instruments on the James Webb Space Telescope. To characterize the atmospheric parameters, we utilize two atmospheric model grids: the Sonora Elf Owl and ATMO2020++. The effective temperatures derived from the two models are relatively consistent, and metallicities are both close to solar values. However, significant discrepancies are found in other parameters, particularly in surface gravity, with the values obtained from the Sonora Elf Owl models typically being about 1 dex lower than those from the ATMO2020++ models. Further comparisons using the ATMO2020 models highlight that the adiabatic convective process introduced in the ATMO2020++ models has a significant impact on the determination of surface gravity. Using the fitted effective temperatures and absolute parallaxes from the literature, we derive radii for the brown dwarfs, which range from approximately 0.8 to 1.2 $R_{\mathrm{Jup}}$. The estimated masses and ages, derived using evolutionary tracks, indicate that most brown dwarfs in our sample have masses below 30 $M_{\mathrm{Jup}}$ and are younger than 6 Gyr. Specifically, Y dwarfs have masses ranging from 2 to 20 $M_{\mathrm{Jup}}$ and ages between 0.1 and 6.7 Gyr. In addition, We discuss the determination of atmospheric parameters using only NIRSpec or MIRI spectra. Comparisons with results from the combined spectra show that the effective temperatures and surface gravities derived solely from NIRSpec spectra are largely consistent with those obtained from the combined spectra.

arXiv comment31 pages, 14 figures, accepted for publication in ApJ

References in corpus (45)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
• WFPC2 Stellar Photometry with HSTphot
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope I. Overview of the instrument and its capabilities
• An Infrared Spectroscopic Sequence of M, L and T Dwarfs
• Abundances of the elements in the solar system
• A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
• Towards Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis
• 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)
• Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• Infrared Parallaxes for Methane T dwarfs
• A statistical test for Nested Sampling algorithms
• Collaborative Nested Sampling: Big Data vs. complex physical models
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets
• A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs
• Cloudless atmospheres for L/T dwarfs and extra-solar giant planets
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• A Study of the Diverse T Dwarf Population Revealed by WISE
• 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 Mid-Infrared Instrument for the James Webb Space Telescope: IV. The Low Resolution Spectrometer
• Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• The Sonora Substellar Atmosphere Models. IV. Elf Owl: Atmospheric Mixing and Chemical Disequilibrium with Varying Metallicity and C/O Ratios
• Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs
• 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
• Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. II. Emergence and Sedimentation of Silicate Clouds in L Dwarfs, and Analysis of the Full M5--T9 Field Dwarf Spectroscopic Sample
• Nearby M, L, and T Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)
• Impact of a new H/He equation of state on the evolution of massive brown dwarfs. New determination of the hydrogen burning limit
• The Luminosities of the Coldest Brown Dwarfs
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• The Sonora Substellar Atmosphere Models. II. Cholla: A Grid of Cloud-free, Solar Metallicity Models in Chemical Disequilibrium for the JWST Era
• Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool 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
• Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries
• The First JWST Spectral Energy Distribution of a Y dwarf
• Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs
• Physical parameters of T dwarfs derived from high-resolution near-infrared spectra
• Uniform Forward-Modeling Analysis of Ultracool Dwarfs. II. Atmospheric Properties of 55 Late-T Dwarfs
• New Y and T dwarfs from WISE identified by Methane Imaging

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