Uniform Forward-Modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking

Abstract

We present a forward-modeling framework using the Bayesian inference tool Starfish and cloudless Sonora-Bobcat model atmospheres to analyze low-resolution ($R\approx 80-250$) near-infrared ($1.0-2.5$ $\mu$m) spectra of T dwarfs. Our approach infers effective temperatures, surface gravities, metallicities, radii, and masses, and by accounting for uncertainties from model interpolation and correlated residuals due to instrumental effects and modeling systematics, produces more realistic parameter posteriors than traditional (${\chi }^2$-based) spectral-fitting analyses. We validate our framework by fitting the model atmospheres themselves and finding negligible offsets between derived and input parameters. We apply our methodology to three well-known benchmark late-T dwarfs, HD 3651B, GJ 570D, and Ross 458C, using both solar and non-solar metallicity atmospheric models. We also derive these benchmarks' physical properties using their bolometric luminosities, their primary stars' ages and metallicities, and Sonora-Bobcat evolutionary models. Assuming the evolutionary-based parameters are more robust, we find our atmospheric-based, forward-modeling analysis produces two outcomes. For HD 3615B and GJ 570D, spectral fits provide accurate $T_{\mathrm{eff}}$ and $R$ but underestimated $\log g$ (by $\approx 1.2$ dex) and $Z$ (by $\approx 0.35$ dex), likely due to the systematics from modeling the potassium line profiles. For Ross 458C, spectral fits provide accurate $\log g$ and $Z$ but overestimated $T_{\mathrm{eff}}$ (by $\approx 120$ K) and underestimated $R$ (by $\approx 1.6\times$), likely because our model atmospheres lack clouds, reduced vertical temperature gradients, or disequilibrium processes. Finally, the spectroscopically inferred masses of these benchmarks are all considerably underestimated.

arXiv commentAccepted by ApJ. Minor updates since v1: (1) calculation of (very small) effect by different photometric calibrations (Sec 4.1.6), (2) expanded literature review about possible systematics in evolutionary models (Sec 6), (3) examination of the (very small) difference between Sonora vs ATMO models for luminosity calculations (footnote 10), (4) slight revision to calculation plotted in Figure 2

References in corpus (148)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Gaia mission
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• A Non-Gray Theory of Extrasolar Giant Planets and Brown Dwarfs
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
• Spectroscopic [Fe/H] for 98 extra-solar planet-host stars: Exploring the probability of planet formation
• Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
• Ages for illustrative field stars using gyrochronology: viability, limitations and errors
• Precipitating Condensation Clouds in Substellar Atmospheres
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres
• The UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
• On the rotational evolution of solar- and late-type stars, its magnetic origins, and the possibility of stellar gyrochronology
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• Chromospheric CaII Emission in Nearby F, G, K, and M stars
• Infrared Transmission Spectroscopy of the Exoplanets HD209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope
• BANYAN. XI. The BANYAN $\Sigma$ multivariate Bayesian algorithm to identify members of young associations within 150 pc
• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I
• Late-type stars members of young stellar kinematic groups - I. Single stars
• Neglected Clouds in T and Y Dwarf Atmospheres
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• The Discovery of Y Dwarfs Using Data from the Wide-field Infrared Survey Explorer (WISE)
• L and T Dwarf Models and the L to T Transition
• 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
• Structure and Evolution of Nearby Stars with Planets II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
• Clouds and Chemistry: Ultracool Dwarf Atmospheric Properties from Optical and Infrared Colors
• S4N: A Spectroscopic Survey of Stars in the Solar Neighborhood
• Atmospheric Parameters of Field L and T Dwarfs
• Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B
• The 2MASS Wide-Field T Dwarf Search. III. Seven New T Dwarfs and Other Cool Dwarf Discoveries
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• Transitions in the cloud composition of hot Jupiters
• A Framework for Characterizing the Atmospheres of Low-Mass Low-Density Transiting Planets
• Reflected Spectra and Albedos of Extrasolar Giant Planets I: Clear and Cloudy Atmospheres
• The Deuterium-Burning Mass Limit for Brown Dwarfs and Giant Planets
• Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs
• The RAVE survey: the Galactic escape speed and the mass of the Milky Way
• Chemical consequences of the C/O ratio on hot Jupiters: Examples from WASP-12b,CoRoT-2b, XO-1b, and HD 189733b
• Masses, Radii, and Cloud Properties of the HR 8799 Planets
• Comparative Planetary Atmospheres: Models of TrES-1 and HD209458b
• Spectroscopic metallicities for planet-host stars: extending the samples
• Population Properties of Brown Dwarf Analogs to Exoplanets
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon
• Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity
• Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
• Discovery of a Brown Dwarf Companion to Gliese 570ABC: A 2MASS T Dwarf Significantly Cooler than Gliese 229B
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• The Near-Infrared and Optical Spectra of Methane Dwarfs and Brown Dwarfs
• The Coyote Universe II: Cosmological Models and Precision Emulation of the Nonlinear Matter Power Spectrum
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• The Disk Population of the Upper Scorpius Association
• Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio
• YREC: The Yale Rotating Stellar Evolution Code
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Scaled solar tracks and isochrones in a large region of the Z-Y plane. II. From 2.5 to 20 solar masses
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets
• Stellar Parameters and Metallicities of Stars Hosting Jovian and Neptunian Mass Planets: A Possible Dependence of Planetary Mass on Metallicity
• Discovery of a warm, dusty giant planet around HIP65426
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs
• Individual Dynamical Masses of Ultracool Dwarfs
• Chemical Clues on the Formation of Planetary Systems: C/O vs Mg/Si for HARPS GTO Sample
• Calculations of the Far-Wing Line Profiles of Sodium and Potassium in the Atmospheres of Substellar-Mass Objects
• An Infrared/X-ray Survey for New Members of the Taurus Star-Forming Region
• Mid-Infrared Photometry of Cold Brown Dwarfs: Diversity in Age, Mass and Metallicity
• The atmospheric parameters and spectral interpolator for the stars of MILES
• No Thermal Inversion and a Solar Water Abundance for the Hot Jupiter HD209458b from HST WFC3 Emission Spectroscopy
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Dynamical Mass of the Substellar Benchmark Binary HD 130948BC
• Molecular Abundances in the Atmosphere of the T Dwarf Gl 229B
• Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs
• Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
• A library of near-infrared integral field spectra of young M-L dwarfs
• Abundances in metal-rich stars - Detailed abundance analysis of 47 G and K dwarf stars with [Me/H] $>$ 0.10 dex
• Measuring the Oblateness and Rotation of Transiting Extrasolar Giant Planets
• Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations
• A large stellar evolution database for population synthesis studies. V. Stellar models and isochrones with CNONa abundance anticorrelations
• Placing the spotted T Tauri star LkCa 4 on an HR diagram
• New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown 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
• K-H_2 Quasi-molecular absorption detected in the T-dwarf epsilon Indi Ba
• Age consistency between exoplanet hosts and field stars
• Clouds in the Coldest Brown Dwarfs: FIRE Spectroscopy of Ross 458C
• The discovery of an M4+T8.5 binary system
• M Dwarf Metallicities and Giant Planet Occurrence: Ironing Out Uncertainties and Systematics
• Cosmic Calibration: Constraints from the Matter Power Spectrum and the Cosmic Microwave Background
• 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
• The Helium abundance and Delta Y / Delta Z in Lower Main Sequence stars
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
• Finding benchmark brown dwarfs to probe the IMF as a function of time
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star
• New neighbours. III. 21 new companions to nearby dwarfs, discovered with adaptive optics
• Physical Properties of Young Brown Dwarfs and Very Low-Mass Stars Inferred from High-Resolution Model Spectra
• The First Ultra-Cool Brown Dwarf Discovered by the Wide-field Infrared Survey Explorer
• The Y-Type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry and Near-Infrared Spectroscopy
• Dust in the Photospheric Environment III. A Fundamental Element in the Characterization of Ultracool Dwarfs
• The properties of the T8.5p dwarf Ross 458C
• The Late-T Dwarf Companion to the Exoplanet Host Star HD 3651: A New Benchmark for Gravity and Metallicity Effects in Ultracool Spectra
• Age Determination for 346 Nearby Stars in the Herschel DEBRIS Survey
• IN-SYNC I: Homogeneous Stellar Parameters from High Resolution APOGEE Spectra for Thousands of Pre-main Sequence Star
• Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry
• Wide, Cool and Ultracool Companions to Nearby Stars from Pan-STARRS1
• Hip 63510C, Hip 73786B, and nine new isolated high proper motion T dwarf candidates from UKIDSS DR6 and SDSS DR7
• A new benchmark T8-9 brown dwarf and a couple of new mid-T dwarfs from the UKIDSS DR5+ LAS
• CFBDSIR J1458+1013B: A Very Cold (>T10) Brown Dwarf in a Binary System
• The Physical Properties of HD 3651B: An Extrasolar Nemesis?
• The GJ 504 system revisited. Combining interferometric, radial velocity, and high contrast imaging data
• AKARI Observations of Brown Dwarfs. III. CO, CO2 and CH4 Fundamental Bands and Physical Parameters
• Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert
• Spectroscopic Detection of Carbon Monoxide in Two Late-type T Dwarfs
• Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters
• Activity and the Li abundances in the FGK dwarfs
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• Chemical enrichment and star formation in the Milky Way disk III. Chemodynamical constraints
• Direct imaging of an ultracool substellar companion to the exoplanet host star HD 4113A
• A Dynamical Mass of $70\pm 5$ Jupiter Masses for Gliese 229B, the First T Dwarf
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: IV Upper Sco
• Orbit and Dynamical Mass of the Late-T Dwarf Gl 758 B
• Two intermediate-mass transiting brown dwarfs from the TESS mission
• Planets Around Low-Mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-Mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• WISE J072003.20-084651.2B Is A Massive T Dwarf
• COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-Gravity T4 Benchmark around an Old White Dwarf and A Re-Examination of the Surface-Gravity Dependence of the L/T Transition
• The Pan-STARRS1 Proper-motion Survey for Young Brown Dwarfs in Nearby Star-forming Regions. I. Taurus Discoveries and a Reddening-free Classification Method for Ultracool Dwarfs
• A Significant Over-Luminosity in the Transiting Brown Dwarf CWW 89Ab
• Physical parameters of T dwarfs derived from high-resolution near-infrared spectra
• An Eclipsing Substellar Binary in a Young Triple System discovered by SPECULOOS
• WISE2150-7520AB: A very low mass, wide co-moving brown dwarf system discovered through the citizen science project Backyard Worlds: Planet 9
• Exploring H${}_2$O Prominence in Reflection Spectra of Cool Giant Planets
• A Novel Survey for Young Substellar Objects with the W-band filter II. The Coolest and Lowest Mass Members of the Serpens-South Star-forming Region
• Hunting for brown dwarf binaries and testing atmospheric models with X-Shooter
• Benchmark Transiting Brown Dwarf LHS 6343 C: Spitzer Secondary Eclipse Observations Yield Brightness Temperature and mid-T Spectral Class

Cited by in corpus (16)

• The SPHINX M-dwarf Spectral Grid. I. Benchmarking New Model Atmospheres to Derive Fundamental M-Dwarf Properties
• Retrieving the C and O Abundances of HR 7672~AB: a Solar-Type Primary Star with a Benchmark Brown Dwarf
• Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades
• Retrieval Study of Brown Dwarfs Across the L-T Sequence
• Uniform Forward-Modeling Analysis of Ultracool Dwarfs. II. Atmospheric Properties of 55 Late-T Dwarfs
• The ESO SupJup Survey I: Chemical and isotopic characterisation of the late L-dwarf DENIS J0255-4700 with CRIRES${}^{+}$
• The puzzle of the formation of T8 dwarf Ross 458c
• Enabling Robust Exoplanet Atmospheric Retrievals with Gaussian Processes
• The ESO SupJup Survey VIII. Chemical fingerprints of young L dwarf twins
• X-SHYNE: X-Shooter spectra of young exoplanet analogs II. Presentation and analysis of the full library
• COol Companions ON Ultrawide orbiTS (COCONUTS). III. A Very Red L6 Benchmark Brown Dwarf around a Young M5 Dwarf
• Orbital Modeling of HII 1348B: An Eccentric Young Substellar Companion in the Pleiades
• HD 143811 AB b: A Directly Imaged Planet Orbiting a Spectroscopic Binary in Sco-Cen
• The Sonora Brown Dwarf Atmosphere and Evolution Models I. Model Description and Application to Cloudless Atmospheres in Rainout Chemical Equilibrium
• Effects of Rotation on the Spectra of Brown Dwarfs
• A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late-T Dwarfs