TOI-1759 b: A transiting sub-Neptune around a low mass star characterized with SPIRou and TESS^★,★★

¹ Institut d’Astrophysique de Paris, CNRS, UMR 7095, Sorbonne Université, 98 bis bd Arago, 75014 Paris, France
e-mail: martioli@iap.fr
² Laoratório Nacional de Astrofísica, Rua Estados Unidos 154, 37504-364 Itajubá, MG, Brazil
³ Observatoire de Haute Provence, St Michel l’Observatoire, France
⁴ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, IRAP/UMR 5277, 14 avenue Edouard Belin, 31400, Toulouse, France
⁵ Université de Montréal, Département de Physique, IREX, Montréal, QC H3C 3J7, Canada
⁶ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁷ Canada-France-Hawaii Telescope, CNRS, 96743 Kamuela, Hawaii, USA
⁸ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
¹⁰ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Natal, RN 59072–970, Brazil
¹¹ Université de Montpellier, CNRS, LUPM, 34095 Montpellier, France
¹² Science Division, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹³ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹⁴ Observatori Astronòmic Albanyà, Camí de Bassegoda s/n, Albanyà 17733, Girona, Spain
¹⁵ Grand Pra Observatory, 1984 Les Haudères, Switzerland
¹⁶ Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA
¹⁸ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁹ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²⁰ NASA Ames Research Center, Moffett Field, CA 94035, USA
²¹ Department of Astrophysical Sciences, Peyton Hall, 4 Ivy Lane, Princeton, NJ 08544, USA
²² LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
²³ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁴ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²⁵ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
²⁶ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150–762 Porto, Portugal
²⁷ U.S. Naval Observatory, Washington, DC 20392, USA
²⁸ Institute of Astronomy and Astrophysics, Academia Sinica 11F of Astronomy-Mathematics Building No. 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan ROC
²⁹ SETI Institute, 189 Bernardo Ave., Suite 200, Mountain View, CA 94043, USA
³⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³¹ NASA Exoplanet Science Institute, Caltech IPAC, 1200 E. California Blvd., Pasadena, CA 91125, USA
³² Physics & Astronomy Department, University of Kansas, Lawrence, KS, USA
³³ Observatoire de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
³⁴ International Center for Advanced Studies (ICAS) and ICIFI (CONICET), ECyT-UNSAM, Campus Miguelete, 25 de Mayo y Francia, (1650), Buenos Aires, Argentina
³⁵ Institut de Recherche sur les Exoplanètes, Département de Physique, Université de Montréal, 1375 Avenue Thérèse-Lavoie-Roux, Montreal, QC H2V 0B3, Canada
³⁶ Department of Physics & Space Science, Royal Military College of Canada, PO Box 17000 Station Forces, Kingston, ON K7K 0C6, Canada
³⁷ Tartu Observatory, University of Tartu, Observatooriumi 1, Tõravere, 61602 Tartumaa, Estonia

Received: 28 October 2021
Accepted: 2 February 2022

Abstract

We report the detection and characterization of the transiting sub-Neptune TOI-1759 b, using photometric time series from the Transiting Exoplanet Survey Satellite (TESS) and near-infrared spectropolarimetric data from the Spectro-Polarimètre Infra Rouge (SPIRou) on the Canada-France-Hawaii Telescope. TOI-1759 b orbits a moderately active M0V star with an orbital period of 18.849975 ± 0.000006 days, and we measured a planetary radius and mass of 3.06 ± 0.22 R_⊕ and 6.8 ± 2.0 M_⊕. Radial velocities were extracted from the SPIRou spectra using both the cross-correlation function and the line-by-line methods, optimizing the velocity measurements in the near-infrared domain. We analyzed the broadband spectral energy distribution of the star and the high-resolution SPIRou spectra to constrain the stellar parameters and thus improve the accuracy of the derived planet parameters. A least squares deconvolution analysis of the SPIRou Stokes V polarized spectra detects Zeeman signatures in TOI-1759. We modeled the rotational modulation of the magnetic stellar activity using a Gaussian process regression with a quasi-periodic covariance function and find a rotation period of 35.65_−0.15^+0.17 days. We reconstructed the large-scale surface magnetic field of the star using Zeeman-Doppler imaging, which gives a predominantly poloidal field with a mean strength of 18 ± 4 G. Finally, we performed a joint Bayesian Markov chain Monte Carlo analysis of the TESS photometry and SPIRou radial velocities to optimally constrain the system parameters. At 0.1176 ± 0.0013 au from the star, the planet receives 6.4 times the bolometric flux incident on Earth, and its equilibrium temperature is estimated at 433 ± 14 K. TOI-1759 b is a likely gas-dominated sub-Neptune with an expected high rate of photoevaporation. Therefore, it is an interesting target to search for neutral hydrogen escape, which may provide important constraints on the planetary formation mechanisms responsible for the observed sub-Neptune radius desert.