Fingering convection and cloudless models for cool brown dwarf atmospheres

Abstract

This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g. other types of clouds or internal energy transport mechanisms. We use a one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH3 quenching are taken into account. T dwarf spectra still have some reddening in e.g. J - H compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.

Accepted in ApJL

References in corpus (10)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• A chemical model for the atmosphere of hot Jupiters
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• Water Clouds in Y Dwarfs and Exoplanets
• A Systematic Study of Departures from Chemical Equilibrium in the Atmospheres of Substellar Mass Objects
• Layered convection as the origin of Saturn's luminosity anomaly
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• An independent analysis of the brown dwarf atmosphere monitoring (BAM) data: large-amplitude variability is rare outside the L/T transition
• The Luminosities of the Coldest Brown Dwarfs

Cited by in corpus (54)

• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• An ultrahot gas-giant exoplanet with a stratosphere
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance
• The Complete transmission spectrum of WASP-39b with a precise water constraint
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• A hybrid line list for CH${}_4$ and hot methane continuum
• The Effects of Consistent Chemical Kinetics Calculations on the Pressure-Temperature Profiles and Emission Spectra of Hot Jupiters
• Treatment of overlapping gaseous absorption with the correlated-k method in hot Jupiter and brown dwarf atmosphere models
• The UK Met Office GCM with a sophisticated radiation scheme applied to the hot Jupiter HD 209458b
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Helios-r2 -- A new Bayesian, open-source retrieval model for brown dwarfs and exoplanet atmospheres
• An emission spectrum for WASP-121b measured across the 0.8-1.1 micron wavelength range using the Hubble Space Telescope
• Toward the analysis of JWST exoplanet spectra: Identifying troublesome model parameters
• A Uniform Retrieval Analysis of Ultracool Dwarfs. III. Properties of Y-Dwarfs
• Signatures of Strong Magnetization and Metal-Poor Atmosphere for a Neptune-Size Exoplanet
• Thermo-compositional diabatic convection in the atmospheres of brown dwarfs and in Earth's atmosphere and oceans
• Diurnal variations in the stratosphere of the ultrahot giant exoplanet WASP-121b
• Updated Parameters and a New Transmission Spectrum of HD 97658b
• Confirmation of water emission in the dayside spectrum of the ultrahot Jupiter WASP-121b
• A new chemical scheme for giant planet thermochemistry. Update of the methanol chemistry and new reduced chemical scheme
• A Library of Self-Consistent Simulated Exoplanet Atmospheres
• Water and an escaping helium tail detected in the hazy and methane-depleted atmosphere of HAT-P-18b from JWST NIRISS/SOSS
• Cloudless atmospheres for young low-gravity substellar objects
• Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parameterised, phase-equilibrium cloud formation code EddySed
• The Impending Opacity Challenge in Exoplanet Atmospheric Characterization
• Hubble PanCET: An isothermal day-side atmosphere for the bloated gas-giant HAT-P-32Ab
• Observed Variability at 1um and 4um in the Y0 Brown Dwarf WISEP J173835.52+273258.9
• The Second Discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) Program: A Cold Wide-Orbit Exoplanet around a Young Field M Dwarf at 10.9 pc
• CO or no CO? Narrowing the CO abundance constraint and recovering the H2O detection in the atmosphere of WASP-127 b using SPIRou
• 15NH3 in the atmosphere of a cool brown dwarf
• Transmission Spectroscopy of WASP-79b from 0.6 to 5.0 $\mu$m
• The Impact of Mixing Treatments on Cloud Modelling in 3D Simulations of Hot Jupiters
• Retrieval Study of Brown Dwarfs Across the L-T Sequence
• A reduced chemical scheme for modelling warm to hot hydrogen-dominated atmospheres
• The carbon-to-oxygen ratio: implications for the spectra of hydrogen-dominated exoplanet atmospheres
• A Comprehensive Analysis of WASP-17b's Transmission Spectrum from Space-Based Observations
• The HST PanCET Program: An Optical to Infrared Transmission Spectrum of HAT-P-32Ab
• Ground-Based Transmission Spectroscopy with FORS2: A featureless optical transmission spectrum and detection of H${}_2$O for the ultra-hot Jupiter WASP-103b
• Strong H${}_2$O and CO emission features in the spectrum of KELT-20b driven by stellar UV irradiation
• The Impact of Phase Equilibrium Cloud Models on GCM Simulations of GJ~1214b
• GRAVITY K-band spectroscopy of HD 206893 B: brown dwarf or exoplanet
• Evidence of a Clear Atmosphere for WASP-62b: the Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone
• Transmission spectroscopy with VLT FORS2: a featureless spectrum for the low-density transiting exoplanet WASP-88b
• Why is it So Hot in Here? Exploring Population Trends in $\text{Spitzer}$ Thermal Emission Observations of Hot Jupiters using Planet-Specific Self-Consistent Atmospheric Models
• VLTI/GRAVITY Observations and Characterization of the Brown Dwarf Companion HD 72946 B
• The photometric periods of rapidly rotating field ultra-cool dwarfs
• The Hubble PanCET program: Emission spectrum of hot Jupiter HAT-P-41b
• Radiative Transfer and Inversion codes for characterizing planetary atmospheres: an overview
• Informed systematic method to identify variable mid and late-T dwarfs
• On the Utility of Transmission Color Analysis I: Differentiating Super-Earths and Sub-Neptunes
• Global Chemistry and Thermal Structure Models for the Hot Jupiter WASP-43b and Predictions for JWST
• Idealised 3D simulations of diabatically-forced Ledoux convection. Application to the atmosphere of hot rocky exoplanets
• Time-resolved Optical Polarization Monitoring of the Most Variable Brown Dwarf