The GAPS programme at TNG

LXII. Studies of atmospheric FeII winds in ultra-hot Jupiters KELT-9b and KELT-20b using the HARPS-N spectrograph

¹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
² Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
³ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
⁴ University of Palermo, Department of Physics and Chemistry “Emilio Segrè”, Via Archirafi 36, Palermo, Italy
⁵ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
⁶ Dipartimento di Fisica e Astronomia “Galileo Galilei” – Università degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁷ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁸ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁹ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
¹⁰ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
¹¹ Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, Tenerife, Spain
¹² Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

^★ Corresponding author; monika.beata.stangret@gmail.com

Received: 27 June 2024
Accepted: 25 September 2024

Abstract

Ultra-hot Jupiters (UHJs) are gas giant planets orbiting close to their host star, with equilibrium temperatures exceeding 2000 K, and among the most studied planets in terms of their atmospheric composition. Thanks to a new generation of ultra-stable high-resolution spectrographs, it is possible to detect the signal from the individual lines of the species in the exoplanetary atmospheres. We employed two techniques in this study. First, we used transmission spectroscopy, which involved examining the spectra around single lines of Fe II. Then we carried out a set of cross-correlation studies for two UHJs: KELT-9b and KELT-20b. Both planets orbit fast-rotating stars, which resulted in the detection of the strong Rossiter-McLaughlin (RM) effect and center-to-limb variations in the transmission spectrum. These effects had to be corrected to ensure a precise analysis. Using the transmission spectroscopy method, we detected 21 single lines of Fe II in the atmosphere of KELT-9b. All of the detected lines are blue-shifted, suggesting strong day-to-night side atmospheric winds. The cross-correlation method leads to the detection of the blue-shifted signal with a signal-to-noise ratio (S/N) of 13.46. Our results are in agreement with models based on non-local thermodynamical equilibrium (NLTE) effects, with a mean micro-turbulence of ν_mic = 2.73 ± 1.5 km s⁻¹ and macro-turbulence of ν_mac = 8.22 ± 3.85 km s⁻¹. In the atmosphere of KELT-20b, we detected 17 single lines of Fe II. Considering different measurements of the systemic velocity of the system, we conclude that the existence of winds in the atmosphere of KELT-20b cannot be determined conclusively. The detected signal with the cross-correlation method presents a S/N of 11.51. The results are consistent with NLTE effects, including means of ν_mic = 3.04 ± 0.35 km s⁻¹ and ν_mac = 6.76 ± 1.17 km s⁻¹.