The GAPS Programme at TNG

Abstract

Context. Giant planets in short-period orbits around bright stars represent optimal candidates for atmospheric and dynamical studies of exoplanetary systems. Aims. We aim to analyse four transits of WASP-33b observed with the optical high-resolution HARPS-N spectrograph to confirm its nodal precession, study its atmosphere, and investigate the presence of star-planet interactions. Methods. We extracted the mean line profiles of the spectra using the least-squares deconvolution method, and we analysed the Doppler shadow and the radial velocities. We also derived the transmission spectrum of the planet, correcting it for the stellar contamination due to rotation, centre-to-limb variations, and pulsations. Results. We confirm the previously discovered nodal precession of WASP-33b, almost doubling the time coverage of the inclination and projected spin-orbit angle variation. We find that the projected obliquity reached a minimum in 2011, and we used this constraint to derive the geometry of the system, and in particular its obliquity at that epoch (ϵ = 113.99° ± 0.22°) and the inclination of the stellar spin axis (is = 90.11° ± 0.12°). We also derived the gravitational quadrupole moment of the star J2 = (6.73 ± 0.22) × 10−5, which we find to be in close agreement with the theoretically predicted value. Small systematics errors are computed by shifting the date of the minimum projected obliquity. We present detections of Hα and Hβ absorption in the atmosphere of the planet, with a contrast almost twice as small as that previously detected in the literature. We also find evidence for the presence of a pre-transit signal, which repeats in all four analysed transits and should thus be related to the planet. The most likely explanation lies in a possible excitation of a stellar pulsation mode by the presence of the planetary companion. Conclusions. A future common analysis of all available datasets in the literature will help shed light on the possibility that the observed Balmer lines’ transit depth variations are related to stellar activity and pulsation, and to set constraints on the planetary temperature–pressure structure and thus on the energetics possibly driving atmospheric escape. A complete orbital phase coverage of WASP-33b with high-resolution spectroscopic (and spectro-polarimetric) observations could help us to understand the nature of the pre-transit signal.

Nodal Precession and Tidal Evolution of Two Hot-Jupiters: WASP-33 b and KELT-9 b

“…One of the goals of this study was to improve upon the established results for the orbital parameters of WASP-33 b and KELT-9 b by previous works (e.g., Johnson et al 2015;Gaudi et al 2017;Watanabe et al 2020), given the longer baseline for observations and making use of the measured nodal precession of the planets' orbits. As such, we confirm for WASP-33 b that i * is close to 90 deg, and determine a best-fit value for J 2 significantly lower compared to previous works with shorter baselines (e.g., Watanabe et al 2020), and consistent with recent work with similar extended baseline coverage (Borsa et al 2021) (see also Table 3).…”

“…We model the observed changes of the projected obliquity λ and impact parameter b over time, assuming pre-cession of the nodes due to tidal interactions between the planets and their host stars. Our analysis is similar to that discussed in previous works (e.g., Watanabe et al 2020;Borsa et al 2021). We translate the observed values of λ and b into values for the ascending node versus the line-of-sight, Ω, and the inclination of the planetary orbital plane versus the plane of the sky, I, via the equations tan Ω = − sin λ tan i p…”

“…Because the Subaru observation was bracketed by the two ends of the time baseline from 2008 to 2019, the Subaru data are non-essential in the subsequent analyses. For a similar reason, we do not include archival data from HARPS-N that span from 2016 to 2019 (Borsa et al 2021).…”

“…These exoplanets are among the hottest exoplanets that have been discovered over recent decades, orbiting stars with effective temperatures above 7400 K and 10, 000 K, respectively (e.g., Collier Cameron et al 2010a;Gaudi et al 2017). Both planets have been extensively studied by previous works, investigating among other factors their orbits and atmospheres (e.g., Collier Cameron et al 2010a;von Essen et al 2014;Johnson et al 2015;Gaudi et al 2017;Ahlers et al 2020;Watanabe et al 2020;Borsa et al 2021;Pai Asnodkar et al 2022a,b), and are known to have large spin-orbit misalignments. In this work we obtain new data to extend the timeline of nodal precession measurements by several years for both planets compared to previous works (see Sections 2 and 3.3), allowing us to derive more accurate tidal parameters for both systems (see Section 4).…”

Gravity darkening and tidally perturbed stellar pulsation in the misaligned exoplanet system WASP-33

“…The planetary companion of WASP-33 is a hot Jupiter (P ∼ 1.219867 ± 4.2 • 10 −5 days (von Essen et al 2020), M P ∼ 2.10 ± 0.14M J , R P ∼ 1.59 ± 0.07R J (Chakrabarty & Sengupta 2019)). WASP-33b (Christian et al 2006) was the first confirmed planet orbiting a δ Sct host star (Herrero et al 2011), and it has been analyzed thoroughly including Doppler tomography and radial velocity measurements (Collier Cameron et al 2010;Watanabe et al 2020;Borsa et al 2021) as well as ground-based photometry (von Essen et al 2014). Using the TESS light curve, von Essen et al (2020) improved the precision of the known transit parameters.…”