Directly imaged L-T transition exoplanets in the mid-infrared

Andrew J. Skemer, Mark S. Marley, Philip M. Hinz, Katie M. Morzinski, Michael F. Skrutskie, Jarron M. Leisenring, Laird M. Close, Didier Saumon, Vanessa P. Bailey, Runa Briguglio, Denis Defrere, Simone Esposito, Katherine B. Follette, John M. Hill, Jared R. Males, Alfio Puglisi, Timothy J. Rodigas, Marco Xompero

Research output: Contribution to journalArticlepeer-review

83 Scopus citations

Abstract

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 and vertical mixing presents a picture of dynamic planetary atmospheres in which both horizontal and vertical motions influence the chemical and condensate profiles.

Original languageEnglish (US)
Article number17
JournalAstrophysical Journal
Volume792
Issue number1
DOIs
StatePublished - Sep 1 2014

Keywords

  • brown dwarfs
  • infrared: planetary systems
  • instrumentation: adaptive optics
  • planets and satellites: atmospheres
  • planets and satellites: gaseous planets
  • stars: individual (HR 8799, 2M1207 b)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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