Clouds and chemistry in the atmosphere of extrasolar planet HR8799b

Travis S. Barman, Bruce MacIntosh, Quinn M. Konopacky, Christian Marois

Research output: Contribution to journalArticle

194 Scopus citations

Abstract

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 narrowband 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 CH4 absorption is detected at K band, indicating efficient vertical mixing and a disequilibrium CO/CH4 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 eff = 1100K ± 100 and log (g) = 3.5 ± 0.5 (for solar composition). Given the observed luminosity (log L obs/L ∼ - 5.1), these values correspond to a radius of 0.75 R Jup +0.17 - 0.12 and a mass of ∼0.72 M Jup +2.6 - 0.6 - strikingly inconsistent with interior/evolution models. Enhanced metallicity (up to ∼10× 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.

Original languageEnglish (US)
Article number65
JournalAstrophysical Journal
Volume733
Issue number1
DOIs
StatePublished - May 20 2011

Keywords

  • brown dwarfs
  • planetary systems
  • stars: atmospheres
  • stars: low-mass

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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