2015A&A...584A..75V

We observed a secondary eclipse of WASP-33 b quasi-simultaneously in the optical (∼0.55µm) and the near-infrared (∼1.05µm) using the 2x8.4m Large Binocular Telescope. WASP-33 is a δ Scuti star pulsating with periods comparable to the eclipse duration, making the determination of the eclipse depth challenging. We use previously determined oscillation frequencies to model and remove the pulsation signal from the light curves, isolating the secondary eclipse. The determined eclipse depth is ΔF=1.03±0.34 parts per thousand, corresponding to a brightness temperature of T_B=3398±302K. Combining previously published data with our new measurement we find the equilibrium temperature of WASP-33 b to be T_B=3358±165K. We compare all existing eclipse data to a blackbody spectrum, to a carbon-rich non-inverted model and to a solar composition model with an inverted temperature structure. We find that current available data on WASP-33 b's atmosphere can be best represented by a simple blackbody emission, without the need for more sophisticated atmospheric models with temperature inversions. Although our data cannot rule out models with or without a temperature inversion, they do confirm a high brightness temperature for the planet at short wavelengths. WASP-33 b is one of the hottest exoplanets known till date, and its equilibrium temperature is consistent with rapid reradiation of the absorbed stellar light and a low albedo.