CHEOPS observations confirm nodal precession in the WASP-33 system
Alonso, R.; Deleuil, M.; Erikson, A.; Fridlund, M.; Queloz, D.; Rauer, H.; Olofsson, G.; Wolf, S.; Pallé, E.; Ribas, I.; Güdel, M.; Isaak, K. G.; Scandariato, G.; Pagano, I.; Baumjohann, W.; Derekas, A.; Gandolfi, D.; Fossati, L.; Korth, J.; Csizmadia, Sz.; Smith, A. M. S.; Cabrera, J.; Persson, C. M.; Ségransan, D.; Walton, N. A.; Ragazzoni, R.; Piotto, G.; Egger, J. A.; Benz, W.; Deline, A.; Collier Cameron, A.; Alibert, Y.; Fortier, A.; Hoyer, S.; Bonfanti, A.; Salmon, S.; Sousa, S. G.; Wilson, T. G.; Bárczy, T.; Barrado, D.; Barros, S. C. C.; Billot, N.; Borsato, L.; Brandeker, A.; Broeg, C.; Davies, M. B.; Demangeon, O. D. S.; Demory, B. -O.; Ehrenreich, D.; Gillon, M.; Harre, J. -V.; Hooton, M. J.; Kiss, L. L.; Lam, K. W. F.; Laskar, J.; Lecavelier des Etangs, A.; Lendl, M.; Magrin, D.; Maxted, P. F. L.; Nascimbeni, V.; Ottensamer, R.; Peter, G.; Pollacco, D.; Rando, N.; Santos, N. C.; Simon, A. E.; Szabó, Gy. M.; Udry, S.; Van Grootel, V.; Helling, Ch.; Gazeas, K.; Merín, B.; Sulis, S.; Viotto, V.; Cubillos, P. E.; Correia, A. C. M.; Asquier, J.; Günther, M. N.; Heitzmann, A.; Mordasini, C.; Piazza, D.; Stalport, M.; Venturini, J.; Villaver, E.; Walter, I.; Hasiba, J.; Ulmer-Moll, S.; Edwards, B.; Kalman, Sz.
Germany, Belgium, Switzerland, Sweden, Netherlands, Portugal, Austria, United Kingdom, France, Hungary, Spain, Italy, Greece
Abstract
Aims. We aim to observe the transits and occultations of WASP-33 b, which orbits a rapidly rotating δ Scuti pulsator, with the goal of measuring the orbital obliquity via the gravity-darkening effect, and constraining the geometric albedo via the occultation depth. Methods. We observed four transits and four occultations with CHEOPS, and employ a variety of techniques to remove the effects of the stellar pulsations from the light curves, as well as the usual CHEOPS systematic effects. We also performed a comprehensive analysis of low-resolution spectral and Gaia data to re-determine the stellar properties of WASP-33. Results. We measure an orbital obliquity 111.3‑0.7+0.2 degrees, which is consistent with previous measurements made via Doppler tomography. We also measure the planetary impact parameter, and confirm that this parameter is undergoing rapid secular evolution as a result of nodal precession of the planetary orbit. This precession allows us to determine the second-order fluid Love number of the star, which we find agrees well with the predictions of theoretical stellar models. We are unable to robustly measure a unique value of the occultation depth, and emphasise the need for long-baseline observations to better measure the pulsation periods.