An old warm Jupiter orbiting the metal-poor G-dwarf TOI-5542^★

¹ Observatoire de Genève, Université de Genève, 51 Chemin Pegasi, 1290 Versoix, Switzerland
e-mail: nolan.grieves@unige.ch
² Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁴ Vanderbilt University, Department of Physics & Astronomy, 6301 Stevenson Center Lane, Nashville, TN 37235, USA
⁵ NASA Ames Research Center, Moffett Field, CA 94035, USA
⁶ School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
⁷ Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁸ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
⁹ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁰ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹¹ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, 7941169 Santiago, Chile
¹² Millennium Institute for Astrophysics, Camino El Observatorio 1515, Las Condes, Casilla, Santiago, Chile
¹³ Instituto de Astronomía, Universidad Católica del Norte, Angamos 0610, 1270709 Antofagasta, Chile
¹⁴ Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
¹⁵ South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa
¹⁶ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Received: 20 May 2022
Accepted: 19 September 2022

Abstract

We report the discovery of a 1.32_−0.10^+0.10 M_Jup planet orbiting on a 75.12 day period around the G3V 10.8_−3.6^+2.1 Gyr old star TOI-5542 (TIC 466206508; TYC 9086-1210-1). The planet was first detected by the Transiting Exoplanet Survey Satellite (TESS) as a single transit event in TESS Sector 13. A second transit was observed 376 days later in TESS Sector 27. The planetary nature of the object has been confirmed by ground-based spectroscopic and radial velocity observations from the CORALIE and HARPS spectrographs. A third transit event was detected by the ground-based facilities NGTS, EulerCam, and SAAO. We find the planet has a radius of 1.009_−0.035^+0.036 R_Jup and an insolation of 9.6_−0.8^+0.9 S_⊕, along with a circular orbit that most likely formed via disk migration or in situ formation, rather than high-eccentricity migration mechanisms. Our analysis of the HARPS spectra yields a host star metallicity of [Fe/H] = −0.21 ± 0.08, which does not follow the traditional trend of high host star metallicity for giant planets and does not bolster studies suggesting a difference among low- and high-mass giant planet host star metallicities. Additionally, when analyzing a sample of 216 well-characterized giant planets, we find that both high masses (4 M_Jup < M_p < 13 M_Jup) and low masses (0.5 M_Jup < M_p < 4 M_Jup), as well as both both warm (P > 10 days) and hot (P < 10 days) giant planets are preferentially located around metal-rich stars (mean [Fe/H] > 0.1). TOI-5542b is one of the oldest known warm Jupiters and it is cool enough to be unaffected by inflation due to stellar incident flux, making it a valuable contribution in the context of planetary composition and formation studies.