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Title: Directly imaged L-T transition exoplanets in the mid-infrared {sup ,}

Gas-giant planets emit a large fraction of their light in the mid-infrared (≳3 μm), where photometry and spectroscopy are critical to our understanding of the bulk properties of extrasolar planets. Of particular importance are the L- and M-band atmospheric windows (3-5 μm), which are the longest wavelengths currently accessible to ground-based, high-contrast imagers. We present binocular LBT adaptive optics (AO) images of the HR 8799 planetary system in six narrow-band filters from 3 to 4 μm, and a Magellan AO image of the 2M1207 planetary system in a broader 3.3 μm band. These systems encompass the five known exoplanets with luminosities consistent with L → T transition brown dwarfs. Our results show that the exoplanets are brighter and have shallower spectral slopes than equivalent temperature brown dwarfs in a wavelength range that contains the methane fundamental absorption feature (spanned by the narrow-band filters and encompassed by the broader 3.3 μm filter). For 2M1207 b, we find that thick clouds and non-equilibrium chemistry caused by vertical mixing can explain the object's appearance. For the HR 8799 planets, we present new models that suggest the atmospheres must have patchy clouds, along with non-equilibrium chemistry. Together, the presence of a heterogeneous surface andmore » vertical mixing presents a picture of dynamic planetary atmospheres in which both horizontal and vertical motions influence the chemical and condensate profiles.« less
Authors:
; ; ; ; ; ; ; ; ;  [1] ;  [2] ;  [3] ;  [4] ; ; ; ;  [5] ;  [6]
  1. Steward Observatory, Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
  2. NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States)
  3. Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, VA 22904 (United States)
  4. Los Alamos National Laboratory, Mail Stop F663, Los Alamos, NM 87545 (United States)
  5. Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Arcetri Largo E. Fermi 5 50125 Firenze (Italy)
  6. Large Binocular Telescope Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22365226
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 792; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; EMISSION; EQUILIBRIUM; IMAGES; LUMINOSITY; METHANE; MIXING; OPTICS; PHOTOMETRY; PLANETARY ATMOSPHERES; PLANETS; SATELLITE ATMOSPHERES; SATELLITES; SPECTROSCOPY; STARS; SURFACES; VISIBLE RADIATION; WAVELENGTHS