A sub-Neptune planet around TOI-1695 discovered and characterized with SPIRou and TESS

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: flavien.kiefer@obspm.fr
² Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
³ Observatoire de Haute-Provence, CNRS, Université d’Aix-Marseille, 04870 Saint-Michel-l’Observatoire, France
⁴ LaboratOrio Nacional de Astrofísica, Rua Estados Unidos 154, 37504-364 Itajubá – MG, Brazil
⁵ Université de Montréal, Département de Physique, IREX, Montréal, QC H3C 3J7, Canada
⁶ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, IRAP/UMR 5277, 14 avenue Edouard Belin, 31400 Toulouse, France
⁷ CNRS, IPAG, Université Grenoble Alpes, F-38000 Grenoble, France
⁸ NASA Exoplanet Science Institute, Caltech/IPAC, Pasadena, CA 91125, USA
⁹ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
¹⁰ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹¹ Instituto de Astrofísica e Ciencias do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹² European Southern Observatory, Alonso de Cordova, Vitacura, Santiago, Chile
¹³ Canada-France-Hawaii Telescope, CNRS, 96743 Kamuela, Hawaii, USA
¹⁴ Institut de Recherche sur les Exoplanètes, Département de Physique, Université de Montréal, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, QC H2V 0B3, Canada
¹⁵ Aix-Marseille Univ., CNRS, CNES, Institut Origines, LAM, Marseille, France
¹⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA
¹⁸ Center for Astrophysics, Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
¹⁹ MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁰ Earth and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²¹ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²² NASA Ames Research Center, Moffett Field, CA 94035, USA
²³ SETI Institute, Mountain View, CA 94043, USA
²⁴ Department of Astrophysical Sciences, Peyton Hall, 4 Ivy Lane, Princeton, NJ 08544, USA
²⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
²⁶ LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, 78280 Guyancourt, France
²⁷ Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan
²⁸ Department of Earth Sciences, University of Hawaii at Manoa, Honolulu, Hawaii 96822 USA
²⁹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Lorând Research Network (ELKH), Konkoly- Thege Miklós út 15-17, 1121 Budapest, Hungary
³⁰ CSFK, MTA Centre of Excellence, Budapest, Konkoly Thege Miklós út 15-17, 1121, Hungary
³¹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³² ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
³³ Universidade Federal do Rio Grande do Norte (UFRN), 59078-970, Natal, RN, Brazil
³⁴ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA

Received: 3 October 2022
Accepted: 8 November 2022

Abstract

TOI-1695 is a V-mag = 13 M-dwarf star from the northern hemisphere at 45 pc from the Sun, around which a 3.134-day periodic transit signal from a super-Earth candidate was identified in TESS photometry. With a transit depth of 1.3 mmag, the radius of candidate TOI-1695.01 was estimated by the TESS pipeline to be 1.82 R_⊕ with an equilibrium temperature of ~620 K. We successfully detected a reflex motion of the star and establish that it is due to a planetary companion at an orbital period consistent with the photometric transit period, thanks to a year-long radial-velocity monitoring of TOI-1695 by the SPIRou infrared spectropolarimeter. We used and compared different methods to reduce and analyze those data. We report a 5.5σ detection of the planetary signal, giving a mass of 5.5±1.0 M_⊕ and a radius of 2.03±0.18 R_⊕. We derive a mean equilibrium planet temperature of 590±90 K. The mean density of this small planet of 3.6±1.1 g cm⁻³ is similar (1.7σ lower) than that of the Earth. It leads to a nonnegligible fraction of volatiles in its atmosphere with f_H,He = 0.28_−0.23^+0.46% or f_water = 23±12%. TOI-1695 b is a new sub-Neptune planet at the border of the M-dwarf radius valley that can help test formation scenarios for super-Earth and sub-Neptune-like planets.