3.8 μm Imaging of 400-600 K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB

S. K. Leggett, Trent J. Dupuy, Caroline V. Morley, Mark S. Marley, William M.J. Best, Michael C. Liu, D. Apai, S. L. Casewell, T. R. Geballe, John E. Gizis, J. Sebastian Pineda, Marcia Rieke, G. S. Wright

Research output: Contribution to journalArticle

Abstract

Half of the energy emitted by late-T- A nd Y-type brown dwarfs emerges at 3.5 ≤ λ μm ≤ 5.5. We present new L′ (3.43 ≤ λ μm ≤ 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 λ ∼ 4 μm observations to models, and find that the model fluxes are too low for brown dwarfs cooler than ∼700 K. The discrepancy increases with decreasing temperature, and is a factor of ∼2 at T eff = 500 K and ∼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.

Original languageEnglish (US)
Article number117
JournalAstrophysical Journal
Volume882
Issue number2
DOIs
StatePublished - Sep 10 2019

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Keywords

  • Astrometry-binaries: General-brown dwarfs-infrared: Stars-stars: Atmospheres

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Leggett, S. K., Dupuy, T. J., Morley, C. V., Marley, M. S., Best, W. M. J., Liu, M. C., Apai, D., Casewell, S. L., Geballe, T. R., Gizis, J. E., Pineda, J. S., Rieke, M., & Wright, G. S. (2019). 3.8 μm Imaging of 400-600 K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB. Astrophysical Journal, 882(2), [117]. https://doi.org/10.3847/1538-4357/ab3393