Possible detection of a bimodal cloud distribution in the atmosphere of HAT-P-32\,A\,b from multi-band photometry

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 $\mathit{\text{u}}$-band (350,nm), with an rms scatter of $\approx 1$,mmag. All 11 transits were modelled using $\text{textsc}prism$ and $\text{textsc}gemc$, and the physical properties of the system calculated. We find the mass and radius of the host star to be $1.182\pm 0.041\text{Msun}$ and $1.225\pm 0.015\text{Rsun}$, respectively. For the planet we find a mass of $0.80\pm 0.14\text{Mjup}$, a radius of $1.807\pm 0.022\text{Rjup}$ and a density of $0.126\pm 0.023\text{pjup}$. These values are consistent with those found in the literature. We also obtain a new orbital ephemeris for the system $ T_0 = {\rm BJD/TDB} ,, 2,454,420.447187 (96) ,

• ,2.15000800 (10) \times E $. We measured the transmission spectrum of HAT-P-32,A,b 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-32,A,b.