Possible detection of a bimodal cloud distribution in the atmosphere of HAT-P-32Ab from multi-band photometry

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We present high-precision photometry of eight separate transit events in the HAT-P-32 planetary system. One transit event was observed simultaneously by two telescopes of which one obtained a simultaneous multi-band light curve in three optical bands, giving a total of 11 transit light curves. Due to the filter selection and in conjunction with using the defocussed photometry technique we were able to obtain an extremely high precision, ground-based transit in the u-band (350nm), with an rms scatter of ≈ 1mmag. All 11 transits were modelled using prism and gemc, and the physical properties of the system calculated. We find the mass and radius of the host star to be 1.182± 0.041 and 1.225±0.015, respectively. For the planet we find a mass of 0.80± 0.14, a radius of 1.807±0.022 and a density of 0.126±0.023. These values are consistent with those found in the literature. We also obtain a new orbital ephemeris for the system T₀ = BJD/TDB 2454420.447187 (96) + 2.15000800 (10) × E. We measured the transmission spectrum of HAT-P-32Ab and compared it to theoretical transmission spectra. Our results indicate a bimodal cloud particle distribution consisting of Rayleigh--like haze and grey absorbing cloud particles within the atmosphere of HAT-P-32Ab.