A puffy polar planet

The low density, hot Jupiter TOI-640 b is on a polar orbit^★

¹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: emil@phys.au.dk
² Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁴ Division of Geological and Planetary Sciences, 1200 E California Blvd, Pasadena, CA, 91125, USA
⁵ Department of Astronomy, California Institute of Technology, Pasadena CA 91125, USA
⁶ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
⁷ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁹ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
¹⁰ Center for Planetary Systems Habitability and McDonald Observatory, The University of Texas at Austin, Austin Texas USA 78712, USA
¹¹ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
¹² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹³ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁴ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁵ Department of Astronomy, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo, Japan
¹⁶ Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637, USA
¹⁷ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹⁸ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK

Received: 26 October 2022
Accepted: 28 January 2023

Abstract

TOI-640 b is a hot, puffy Jupiter with a mass of 0.57 ± 0.02 M_J and radius of 1.72 ± 0.05 R_J, orbiting a slightly evolved F-type star with a separation of 6.33_−0.06^+0.07 R_⋆. Through spectroscopic in-transit observations made with the HARPS spectrograph, we measured the Rossiter-McLaughlin effect, analysing both in-transit radial velocities and the distortion of the stellar spectral lines. From these observations, we find the host star to have a projected obliquity of λ = 184 ± 3°. From the TESS light curve, we measured the stellar rotation period, allowing us to determine the stellar inclination, i_⋆ = 23₋₂⁺³°, meaning we are viewing the star pole-on. Combining this with the orbital inclination allowed us to calculate the host star obliquity, ψ = 104 ± 2°. TOI-640 b joins a group of planets orbiting over stellar poles within the range 80°–125°. The origin of this orbital configuration is not well understood.