A large range of haziness conditions in hot-Jupiter atmospheres

Abstract: We present a study of photochemical hazes of exoplanet atmospheres based on a self-consistent model including haze microphysics, disequilibrium chemistry, and radiative feedbacks. We derive the haze properties required to match HST observations of ten hot-Jupiters. HAT-P-12b, HD-189733b, HD-209458b and WASP-6b require haze mass fluxes between 5x10$^{-15}$ and 9x10$^{-12} g.cm^{-2}.s^{-1}$ to match the observations. WASP-12b and WASP-19b with equilibrium temperatures above 2000 K are incompatible with the presence of haze and are better fitted by heavy metals. HAT-P-1b and WASP-31b do not show clear evidence for the presence of hazes with upper mass fluxes of 10$^{-15}$ and 10$^{-16}g.cm^{-2}.s^{-1}$, respectively, while WASP-17b and WASP-39b present an upper mass flux limit of 10$^{-16} g.cm^{-2}.s^{-1}$. We discuss the implications of the self-consistent model and we derive upper limits for the haze abundances based on photochemistry results. Our results suggest HCN as the main haze precursor up to 1300 K effective temperatures and CO above. Our derived haze mass fluxes based on the fit to the observations are consistent with the photochemistry with formation yields up to $\sim$6.4\%. Disequilibrium chemistry has negligible impact on the spectra considering the low resolution observations used but impacts the chemical composition and temperature profiles. We find that hazes produce hotter upper atmosphere temperatures with a detectable impact on the spectra. Clouds may have implications for interpreting the transit spectra of HD-209458b, WASP-31b and WASP-39b. Nevertheless, the presence of silicate and iron clouds is expected in all studied atmospheres except WASP-12b and WASP-19b.