TESS phase curve of ultra-hot Jupiter WASP-189 b

Abstract

The thermal structures of highly irradiated ultra-hot Jupiters can deviate substantially from those of cooler hot Jupiters. For planets orbiting rapidly rotating, and consequently oblate, host stars, photometric light curves provide a unique opportunity to measure the spin-orbit angle. Moreover, in systems with significant spin-orbit misalignment, the stellar oblateness can induce observable orbital precession. We wish to study the atmosphere and orbital architecture of an ultra-hot Jupiter WASP-189 b, orbiting around a hot A-type star. We use the photometric phase curves and gravity-darkened transits of WASP-189 b observed with the Transiting Exoplanet Survey Satellite (TESS), complemented with the archival observations from CHaracterising ExOPlanet Satellite (CHEOPS). We detected a phase curve signal with significant occultation depth of 203.4 (+16.2) (-16.3) ppm, while the nightside flux, -71.8 (+36.4) (-36.0) ppm, is consistent with zero at 2-sigma. We invert the phase curve signal to construct the temperature map of the planet. The map was subsequently used to estimate the Bond albedo and heat redistribution efficiency, the expected median ranges of which are found to be 0.19-0.35 and 0.09-0.41, respectively. Finally, we analysed gravity-darkened transits to find that the planet is in polar orbit with the spin-orbit angle of 89.46 (+1.08) (-1.08) deg. We found no hint of orbital precession while comparing our results with those from the literature. Our observations, together with atmospheric modelling, suggest that the dayside emission of WASP-189 b in TESS and CHEOPS bandpasses is dominated by thermal emission from an atmosphere with extremely inefficient heat transport and negligible contribution from reflected light.