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Thermal emission from WASP-33b, the hottest known planet


  • Based on service observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias.



We report ground-based observations at 0.91 μm of the occultation of the hot Jupiter WASP-33b by its A5 host star. We measure the planet to be 0.109 ± 0.030 per cent as bright as its host star at 0.91 μm. This corresponds to a brightness temperature, TB= 3620+200− 250 K, significantly higher than the zero-albedo equilibrium temperature for both isotropic re-radiation (2750 ± 37 K) and uniform day-side-only re-radiation (3271 ± 44 K), but consistent with the zero-redistribution temperature (3515 ± 47 K). This indicates that the heat redistribution from the day side of WASP-33b to the night side is inefficient and further suggests that there is immediate re-radiation, and therefore little or no redistribution, of heat within the day side. We also detected the stellar pulsations of WASP-33, which we model as the sum of four sinusoids, with periods of between 42 and 77 min and amplitudes of 0.5–1.5 mmag.