Rossiter-McLaughlin detection of the 9-month period transiting exoplanet HIP41378 d

¹ Aix-Marseille Univ., CNRS, CNES, Institut Origines, LAM, Marseille, France
e-mail: salome.grouffal@lam.fr
² Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland
³ Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA
⁴ School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
⁵ Dipartimento di Fisica e Astronomia Galileo Galilei, Vicolo Osservatorio 3, 35122 Padova, Italy
⁶ Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
⁷ Centre for Exoplanets and Habitability, University of Warwick, Coventry, CV4 7AL, UK
⁸ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁹ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹⁰ KICC & Astrophysics Group, Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
¹¹ Centro de Astrobiología (CAB, CSIC-INTA), Depto. de Astrofísica, ESAC campus, 28692, Villanueva de la Canada (Madrid), Spain
¹² INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
¹³ Department of Astronomy, University of California, Berkeley, CA, USA

Received: 3 June 2022
Accepted: 21 October 2022

Abstract

The Rossiter-McLaughlin (RM) effect is a method that allows us to measure the orbital obliquity of planets, which is an important constraint that has been used to understand the formation and migration mechanisms of planets, especially for hot Jupiters. In this paper, we present the RM observation of the Neptune-sized long-period transiting planet HIP41378 d. Those observations were obtained using the HARPS-N/TNG and ESPRESSO/ESO-VLT spectrographs over two transit events in 2019 and 2022. The analysis of the data with both the classical RM and the RM Revolutions methods allows us to confirm that the orbital period of this planet is ~278 days and that the planet is on a prograde orbit with an obliquity of λ = 57.1_−17.9^+26.1°, a value which is consistent between both methods. HIP41378 d is the longest period planet for which the obliquity has been measured so far. We do not detect transit timing variations with a precision of 30 and 100 minutes for the 2019 and 2022 transits, respectively. This result also illustrates that the RM effect provides a solution to follow up on the transit of small and long-period planets such as those that will be detected by ESA's forthcoming PLATO mission.