The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve

Abstract

Context. Gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to those of the coldest stars. These ‘ultra-hot Jupiters’ have atmospheres made of ions and atomic species from molecular dissociation and feature strong day-to-night temperature gradients. Photometric observations at different orbital phases provide insights on the planet’s atmospheric properties. Aims. We aim to analyse the photometric observations of WASP-189 acquired with the Characterising Exoplanet Satellite (CHEOPS) to derive constraints on the system architecture and the planetary atmosphere. Methods. We implemented a light-curve model suited for an asymmetric transit shape caused by the gravity-darkened photosphere of the fast-rotating host star. We also modelled the reflective and thermal components of the planetary flux, the effect of stellar oblateness and light-travel time on transit-eclipse timings, the stellar activity, and CHEOPS systematics. Results. From the asymmetric transit, we measure the size of the ultra-hot Jupiter WASP-189 b, Rp = 1.600−0.016+0.017 RJ, with a precision of 1%, and the true orbital obliquity of the planetary system, Ψp = 89.6 ± 1.2deg (polar orbit). We detect no significant hotspot offset from the phase curve and obtain an eclipse depth of δecl = 96.5−5.0+4.5 ppm, from which we derive an upper limit on the geometric albedo: Ag < 0.48. We also find that the eclipse depth can only be explained by thermal emission alone in the case of extremely inefficient energy redistribution. Finally, we attribute the photometric variability to the stellar rotation, either through superficial inhomogeneities or resonance couplings between the convective core and the radiative envelope. Conclusions. Based on the derived system architecture, we predict the eclipse depth in the upcoming Transiting Exoplanet Survey Satellite (TESS) observations to be up to ~165 ppm. High-precision detection of the eclipse in both CHEOPS and TESS passbands might help disentangle reflective and thermal contributions. We also expect the right ascension of the ascending node of the orbit to precess due to the perturbations induced by the stellar quadrupole moment J2 (oblateness).

The Mantis Network II: examining the 3D high-resolution observable properties of the UHJs WASP-121b and WASP-189b through GCM modelling

“…For the stellar incident flux in the correlated-k radiativetransfer module, we use PHOENIX stellar atmosphere models (Allard et al 2012) interpolated to the properties of WASP-121 (T eff = 6460.0 K, [Fe/H] = 0.13, log g = 3.9) and WASP-189 (Deline et al (2022): T eff = 8000 K, [Fe/H] = 0.29, log g = 3.9) using pysnphot (STScI Development Team 2013).…”

“…However, the K p -V sys signal from each species was different, suggesting chemical inhomogeneity in the atmosphere. Lendl et al (2020) and Deline et al (2022) present CHEOPS pho-tometric data of WASP-189b including an optical phase curve.…”

Phase curve and geometric albedo of WASP-43b measured with CHEOPS, TESS, and HST WFC3/UVIS

“…As discussed in previous analyses (e.g. Deline et al 2022;Hooton et al 2022;Wilson et al 2022), CHEOPS photometry is affected by variable contamination from other stars in the field of view. The variability of this contamination is due to the fact that the Point Spread Function (PSF) of the stars is not circular, and the overlap with the target PSF depends on the roll angle of the telescope (Benz et al 2021).…”

“…One of the main themes of its science program is the characterization of exoplanet atmospheres (Benz et al 2021). This consists of observations of secondary eclipses of hot Jupiters (e.g., Lendl et al 2020;Hooton et al 2022) across a wide range of temperatures and planetary surface gravities, full or partial phase curves of the most compelling targets (e.g., Deline et al 2022), and detailed observations of ultra-hot super-Earths (e.g., Morris et al 2021).…”

“…Lendl et al 2020;Hooton et al 2022) across a wide range of temperatures and planetary surface gravities, full or partial phase curves of the most compelling targets (e.g. Deline et al 2022), and detailed observations of ultra-hot super-Earths (e.g. Morris et al 2021).…”