Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b (original) (raw)
ADS
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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 = 1100 K ±100 and log (g) = 3.5 ± 0.5 (for solar composition). Given the observed luminosity (log L obs/L sun ~ - 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 (<1000 K) required by the evolution models.
Publication:
The Astrophysical Journal
Pub Date:
May 2011
DOI:
arXiv:
Bibcode:
Keywords:
- brown dwarfs;
- planetary systems;
- stars: atmospheres;
- stars: low-mass;
- Astrophysics - Earth and Planetary Astrophysics
E-Print:
17 pages, accepted for publication in The Astrophysical Journal