Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b

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Using the integral field spectrograph OSIRIS, on the Keck II telescope, broad near-infrared H and K-band spectra of the young exoplanet HR8799b have been obtained. In addition, six new narrow-band photometric measurements have been taken across the H and K bands. These data are combined with previously published photometry for an analysis of the planet's atmospheric properties. Thick photospheric dust cloud opacity is invoked to explain the planet's red near-IR colors and relatively smooth near-IR spectrum. Strong water absorption is detected, indicating a Hydrogen-rich atmosphere. Only weak CH{sub 4} absorption is detected at K band, indicating efficient vertical mixing and ... continued below

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Barman, T. S.; Macintosh, B. A.; Konopacky, Q. M. & Marois, C. March 21, 2011.

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Using the integral field spectrograph OSIRIS, on the Keck II telescope, broad near-infrared H and K-band spectra of the young exoplanet HR8799b have been obtained. In addition, six new narrow-band photometric measurements have been taken across the H and K bands. These data are combined with previously published photometry for an analysis of the planet's atmospheric properties. Thick photospheric dust cloud opacity is invoked to explain the planet's red near-IR colors and relatively smooth near-IR spectrum. Strong water absorption is detected, indicating a Hydrogen-rich atmosphere. Only weak CH{sub 4} absorption is detected at K band, indicating efficient vertical mixing and a disequilibrium CO/CH{sub 4} ratio at photospheric depths. The H-band spectrum has a distinct triangular shape consistent with low surface gravity. New giant planet atmosphere models are compared to these data with best fitting bulk parameters, T{sub eff} = 1100K {+-} 100 and log(g) = 3.5 {+-} 0.5 (for solar composition). Given the observed luminosity (log L{sub obs}/L{sub {circle_dot}} {approx} -5.1), these values correspond to a radius of 0.75 R{sub Jup{sub 0.12}{sup +0.17}} and mass {approx} 0.72 M{sub Jup{sub -0.6}{sup +2.6}} - strikingly inconsistent with interior/evolution models. Enhanced metallicity (up to {approx} 10 x that of the Sun) along with thick clouds and non-equilibrium chemistry are likely required to reproduce the complete ensemble of spectroscopic and photometric data and the low effective temperatures (< 1000K) required by the evolution models.

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PDF-file: 19 pages; size: 0.7 Mbytes

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  • Journal Name: Astrophysical Journal, vol. 733, no. 1, May 5, 2011, Article ID 65; Journal Volume: 733; Journal Issue: 1

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  • Report No.: LLNL-JRNL-476433
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 1022142
  • Archival Resource Key: ark:/67531/metadc846698

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  • March 21, 2011

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  • May 19, 2016, 3:16 p.m.

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  • May 31, 2016, 4:08 p.m.

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Barman, T. S.; Macintosh, B. A.; Konopacky, Q. M. & Marois, C. Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b, article, March 21, 2011; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc846698/: accessed December 13, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.