Clouds and chemistry in the atmosphere of extrasolar planet HR8799b.
BARMAN T.S., MACINTOSH B., KONOPACKY Q.M. and MAROIS C.
Abstract (from CDS):
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 CH4absorption 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, Teff = 1100 K ±100 and log (g) = 3.5±0.5 (for solar composition). Given the observed luminosity (log Lobs/L☉∼ - 5.1), these values correspond to a radius of 0.75 RJup+0.17_- 0.12_ and a mass of ∼0.72 MJup+2.6_- 0.6_–strikingly inconsistent with interior/evolution models. Enhanced metallicity (up to ∼10x 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.
brown dwarfs - planetary systems - stars: atmospheres - stars: low-mass
HD20303B is a misprint for HD203030B and J0758+42 is SDSS J075840.33+324723.4 in SIMBAD.