skip to main content

Title: FINGERING CONVECTION AND CLOUDLESS MODELS FOR COOL BROWN DWARF ATMOSPHERES

This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral types 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 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 H{sub 2}-H{sub 2}, H{sub 2}-He, H{sub 2}O, CO, CO{sub 2}, CH{sub 4}, NH{sub 3}, 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 NH{sub 3} 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 coolermore » structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.« less
Authors:
; ; ; ; ;  [1] ;  [2] ;  [3]
  1. Astrophysics Group, University of Exeter, EX4 4QL Exeter (United Kingdom)
  2. Ecole Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, F-69364 Lyon Cedex 07 (France)
  3. Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)
Publication Date:
OSTI Identifier:
22518988
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 804; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMMONIA; CARBON DIOXIDE; CARBON MONOXIDE; CONVECTION; COSMIC DUST; HYDROGEN; IRON; METHANE; OPACITY; PHOTOSPHERE; SILICATES; STELLAR ATMOSPHERES; TEMPERATURE GRADIENTS; TITANIUM OXIDES; VANADIUM OXIDES; WATER