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Cloudless Atmospheres for L/T Dwarfs and Extrasolar Giant PlanetsThe admitted, conventional scenario to explain the complex spectral evolution of brown dwarfs (BDs) since their first detection 20 years ago has always been the key role played by micron-size condensates, called "dust" or "clouds," in their atmosphere. This scenario, however, faces major problems, in particular the J-band brightening and the resurgence of FeH absorption at the L to T transition, and a physical first-principle understanding of this transition is lacking. In this Letter, we propose a new, completely different explanation for BD and extrasolar giant planet (EGP) spectral evolution, without the need to invoke clouds. We show that, due to the slowness of the CO/ CH4 and N2/NH3 chemical reactions, brown dwarf (L and T, respectively) and EGP atmospheres are subject to a thermo-chemical instability similar in nature to the fingering or chemical convective instability present in Earth oceans and at the Earth core/mantle boundary. The induced small-scale turbulent energy transport reduces the temperature gradient in the atmosphere, explaining the observed increase in near-infrared J-H and J-K colors of L dwarfs and hot EGPs, while a warming up of the deep atmosphere along the L to T transition, as the CO/CH4 instability vanishes, naturally solves the two aforementioned puzzles, and provides a physical explanation of the L to T transition. This new picture leads to a drastic revision of our understanding of BD and EGP atmospheres and their evolution.
Document ID
20160001765
Document Type
Reprint (Version printed in journal)
Authors
Tremblin, P. (Exeter Univ. United Kingdom)
Amundsen, D. S. (Exeter Univ. United Kingdom)
Chabrier, G. (Exeter Univ. United Kingdom)
Baraffe, I. (Exeter Univ. United Kingdom)
Drummond, B. (Exeter Univ. United Kingdom)
Hinkley, S. (Exeter Univ. United Kingdom)
Mourier, P. (Ecole Normale Superieure Lyon, France)
Venot, O. (Katholieke Univ. te Leuven Belgium)
Date Acquired
February 11, 2016
Publication Date
January 28, 2016
Publication Information
Publication: The Astrophysical Journal Letters
Volume: 817
Issue: 2
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN29795
Funding Number(s)
CONTRACT_GRANT: 247060-PEPS
CONTRACT_GRANT: IDO/10/2013
CONTRACT_GRANT: 320478-TOFU
CONTRACT_GRANT: NNX14AB99A
CONTRACT_GRANT: WM090065
CONTRACT_GRANT: 247060
Distribution Limits
Public
Copyright
Other
Keywords
Brown dwarf stars
Spectra
Methane