The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations

The hot Jupiter HD 189733 b is the most extensively observed exoplanet. Its atmo-sphere has been detected and characterised 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 atmo-sphere 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 transmis-sion 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