TOI-2084 b and TOI-4184 b: Two new sub-Neptunes around M dwarf stars

¹ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
e-mail: khalid.barkaoui@uliege.be
² Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³ Instituto de Astrofisica de Canarias (IAC), Calle Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain
⁴ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
⁵ Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁶ Instituto de Astrofisica e Ciencias do Espaco, Universidade do porto, CAUP, Rua das Estrelas, 150-762 Porto, Portugal
⁷ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁸ Center for Astrophysics and Space Sciences, UC San Diego, UCSD Mail Code 0424, 9500 Gilman Drive, La Jolla, CA 92093-0424, USA
⁹ Instituto de Astrofisica de Andalucia (IAA-CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain
¹⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
¹¹ NASA Ames Research Center, Moffett Field, CA 94035, USA
¹² Department of Physics & Astronomy, Vanderbilt University, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
¹³ Instituto de Astronomia y Ciencias Planetarias de Atacama, Universidad de Atacama, Copayapu 485, Copiapo, Chile
¹⁴ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁵ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹⁶ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁷ Departamento de Astrofisica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁸ Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁹ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
²⁰ University of St Andrews, Centre for Exoplanet Science, SUPA School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
²¹ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012, Bern, Switzerland
²² School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
²³ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
²⁴ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
²⁵ University of Southern Denmark, University Library, Campusvej 55, 5230 Odense M, Denmark
²⁶ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
²⁷ Centre for ExoLife Sciences, Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5, 1350 Copenhagen, Denmark
²⁸ Universidad Nacional Autonoma de México, Instituto de Astronomia, AP 70-264, Ciudad de México 04510, Mexico
²⁹ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³⁰ Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302-4106, USA
³¹ RECONS Institute, Chambersburg, PA 17201, USA
³² Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³³ Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
³⁴ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³⁵ Universidad Nacional Autonoma de México, Instituto de Astronomia, AP 106, Ensenada 22800, BC, Mexico
³⁶ Department of Physics, Isfahan University of Technology, Isfahan 84156-83111, Iran
³⁷ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
³⁸ South African Astronomical Observatory, PO Box 9, Observatory, Cape Town 7935, South Africa
³⁹ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁴⁰ Kotizarovci Observatory, Sarsoni 90, 51216 Viskovo, Croatia
⁴¹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

Received: 8 May 2023
Accepted: 26 June 2023

Abstract

We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084 b, and TOI-4184b. We characterized the host stars by combining spectra from Shane/Kast and Magellan/FIRE, spectral energy distribution analysis, and stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, and statistical validation packages to support the planetary interpretation. We performed a global analysis of multi-colour photometric data from TESS and ground-based facilities in order to derive the stellar and planetary physical parameters for each system. We find that TOI-2084 band TOI-4184 bare sub-Neptune-sized planets with radii of R_p = 2.47 ± 0.13R_⊕ and R_p = 2.43 ± 0.21 R_⊕, respectively. TOI-2084 b completes an orbit around its host star every 6.08 days, has an equilibrium temperature of T_eq = 527 ± 8 K and an irradiation of S_p = 12.8 ± 0.8 S_⊕. Its host star is a dwarf of spectral M2.0 ± 0.5 at a distance of 114 pc with an effective temperature of T_eff = 3550 ± 50 K, and has a wide, co-moving M8 companion at a projected separation of 1400 au. TOI-4184 b orbits around an M5.0 ± 0.5 type dwarf star (K_mag = 11.87) each 4.9 days, and has an equilibrium temperature of T_eq = 412 ± 8 K and an irradiation of S_p = 4.8 ± 0.4 S_⊕. TOI-4184 is a metal poor star ([Fe/H] = −0.27 ± 0.09 dex) at a distance of 69 pc with an effective temperature of T_eff = 3225 ± 75 K. Both planets are located at the edge of the sub-Jovian desert in the radius-period plane. The combination of the small size and the large infrared brightness of their host stars make these new planets promising targets for future atmospheric exploration with JWST.