Abstract
The hot Jupiter HD 189733b is the most extensively observed exoplanet.
Its atmosphere has been detected and characterized in transmission and
eclipse spectroscopy, and its phase curve measured at several
wavelengths. This paper brings together the results of our campaign to
obtain the complete transmission spectrum of the atmosphere of this
planet from UV to infrared with the Hubble Space Telescope, using the
STIS, ACS and WFC3 instruments. We provide a new tabulation of the
transmission spectrum across the entire visible and infrared range. The
radius ratio in each wavelength band was re-derived, where necessary, to
ensure a consistent treatment of the bulk transit parameters and stellar
limb darkening. Special care was taken to correct for, and derive
realistic estimates of the uncertainties due to, both occulted and
unocculted star spots.
The combined spectrum is very different from the predictions of
cloud-free models for hot Jupiters: it is dominated by Rayleigh
scattering over the whole visible and near-infrared range, the only
detected features being narrow sodium and potassium lines. We interpret
this as the signature of a haze of condensate grains extending over at
least five scaleheights. We show that a dust-dominated atmosphere could
also explain several puzzling features of the emission spectrum and
phase curves, including the large amplitude of the phase curve at 3.6
μm, the small hotspot longitude shift and the hot mid-infrared
emission spectrum. We discuss possible compositions and derive some
first-order estimates for the properties of the putative condensate
haze/clouds. We finish by speculating that the dichotomy between the two
observationally defined classes of hot Jupiter atmospheres, of which HD
189733b and HD 209458b are the prototypes, might not be whether they
possess a temperature inversion, but whether they are clear or dusty. We
also consider the possibility of a continuum of cloud properties between
hot Jupiters, young Jupiters and L-type brown dwarfs.
Original language | English |
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Pages (from-to) | 2917-2944 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 432 |
Issue number | 4 |
DOIs | |
Publication status | Published - 01 Jul 2013 |
Externally published | Yes |
Keywords
- techniques: spectroscopic
- planets and satellites: atmospheres
- stars: individual: HD 189733
- planetary systems