3.8 μm Imaging of 400–600 K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB
AuthorLeggett, S. K.
Dupuy, Trent J.
Morley, Caroline V.
Marley, Mark S.
Best, William M. J.
Liu, Michael C.
Casewell, S. L.
Geballe, T. R.
Gizis, John E.
Pineda, J. Sebastian
Wright, G. S.
AffiliationUniv Arizona, Dept Astron, Steward Observ
Univ Arizona, Dept Planetary Sci, Lunar & Planetary Lab
Univ Arizona, Steward Observ
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationS. K. Leggett et al 2019 ApJ 882 117
RightsCopyright © 2019. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractHalf of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 <= lambda mu m <= 5.5. We present new L' (3.43 <= lambda mu m <= 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L' from spectra for an additional two dwarfs. The targets include two binary systems that were imaged at a resolution of 0.'' 25. One of these, WISEP J045853.90+643452.6AB, shows significant motion, and we present an astrometric analysis of the binary using Hubble Space Telescope, Keck Adaptive Optics, and Gemini images. We compare lambda similar to 4 mu m observations to models, and find that the model fluxes are too low for brown dwarfs cooler than similar to 700 K. The discrepancy increases with decreasing temperature, and is a factor of similar to 2 at T-eff = 500 K and similar to 4 at T-eff = 400 K. Warming the upper layers of a model atmosphere generates a spectrum closer to what is observed. The thermal structure of cool brown dwarf atmospheres above the radiative-convective boundary may not be adequately modeled using pure radiative equilibrium; instead heat may be introduced by thermochemical instabilities (previously suggested for the L- to T-type transition) or by breaking gravity waves (previously suggested for the solar system giant planets). One-dimensional models may not capture these atmospheres, which likely have both horizontal and vertical pressure/temperature variations.
VersionFinal published version
SponsorsNational Aeronautics and Space AdministrationNational Aeronautics & Space Administration (NASA); NASANational Aeronautics & Space Administration (NASA) [NAS 5-26555]; W. M. Keck FoundationW.M. Keck Foundation; NSFNational Science Foundation (NSF) [AST-1518339]