The GAPS Programme at TNG

XXXVI. Measurement of the Rossiter-McLaughlin effect and revising the physical and orbital parameters of the HAT-P-15, HAT-P-17, HAT-P-21, HAT-P-26, HAT-P-29 eccentric planetary systems^★,★★

¹ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
e-mail: lmancini@roma2.infn.it
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁴ Thüringer Landessternwarte, Tautenburg Sternwarte 5, 07778 Tautenburg, Germany
⁵ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
⁶ Astrophysics Group, Keele University, Keele ST5 5BG, UK
⁷ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
⁸ Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
⁹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (Roma), Italy
¹⁰ Observatoire de Genève, Université de Genève, 51 Chemin Pegasi, 1290 Sauverny, Switzerland
¹¹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹² Dipartimento di Fisica e Astronomia “Galileo Galilei” – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹³ INAF – OAS, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy
¹⁴ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
¹⁵ Department of Physics and Astronomy, University of Florence, Largo Enrico Fermi 5, 50125 Firenze, Italy
¹⁶ Instituto de Investigación en Astronomia y Ciencias Planetarias, Universidad de Atacama, Copiapó, Atacama, Chile
¹⁷ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁸ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
¹⁹ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy

Received: 8 April 2022
Accepted: 20 May 2022

Abstract

Context. The measurement of the spin-orbit alignment of hot Jupiters, including a range of orbital and physical properties, can provide information about the evolution of the orbits of this special class of giant planets.

Aims. We aim to refine the orbital and physical parameters and determine the sky-projected planet orbital obliquity λ of five eccentric (e ≅ 0.1–0.3) transiting planetary systems: HAT-P-15, HAT-P-17, HAT-P-21, HAT-P-26, and HAT-P-29, whose parent stars have an effective temperature between 5100 K < T_eff < 6200 K. Each of the systems hosts a hot Jupiter, except for HAT-P-26, which hosts a Neptune-mass planet.

Methods. We observed transit events of these planets with the HARPS-N spectrograph, obtaining high-precision radial velocity measurements that allow us to measure the Rossiter–McLaughlin effect for each of the target systems. We used these new HARPS-N spectra and archival data, including those from Gaia, to better characterise the stellar atmospheric parameters. The photometric parameters for four of the hot Jupiters were recalculated using 17 new transit light curves, obtained with an array of medium-class telescopes, and data from the TESS space telescope. HATNet time-series photometric data were checked for the signatures of rotation periods of the target stars and their spin axis inclination.

Results. From the analysis of the Rossiter-McLaughlin effect, we derived a sky-projected obliquity of λ = 13° ± 6°, λ = −26.3° ± 6.7°, λ = −0.7° ± 12.5°, λ = −26° ± 16°, for HAT-P-15 b, HAT-P-17 b, HAT-P-21 b, and HAT-P-29 b, respectively. Based on theoretical considerations, these small values of λ should be of primordial origin, with the possible exception of HAT-P-21. Due to the quality of the data, we were not able to fully constrain λ for HAT-P-26 b, although a prograde orbit is favoured (λ = 18^° ± 49^°). The stellar activity of HAT-P-21 indicates a rotation period of 15.88 ± 0.02 days, which allowed us to determine its true misalignment angle ψ = 25° ± 16°. Our new analysis of the physical parameters of the five exoplanetary systems returned values compatible with those existing in the literature. Using TESS and the available transit light curves, we reviewed the orbital ephemeris for the five systems and confirmed that the HAT-P-26 system shows transit timing variations, which may tentatively be attributed to the presence of a third body.