The HD 93963 A transiting system: A 1.04 d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS^★

¹ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
e-mail: luisamaria.serrano@unito.it
² Aix Marseille Univ., CNRS, CNES, LAM, 38 rue Frédéric JoliotCurie, 13388 Marseille, France
³ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
⁴ Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
⁵ Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
⁷ Dept. Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁸ NASA Exoplanet Science Institute – Caltech/IPAC, 1200 E. California Blvd, Pasadena, CA 91125, USA
⁹ Space Science and Astrobiology Division NASA Ames Research Center, M/S 245-6, Moffett Field, CA 94035, USA
¹⁰ Center for Space and Habitability, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
¹¹ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
¹² Department of Astronomy, Stockholm University, 106 91 Stockholm, Sweden
¹³ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁴ Lund Observatory, Dept. of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden
¹⁵ Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
¹⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Department of Physics, Shahid Beheshti University, Tehran, Iran
¹⁸ Laboratoire J.-L. Lagrange, Observatoire de la Côte d’Azur (OCA), Université de Nice-Sophia Antipolis (UNS), CNRS, Campus Valrose, 06108 Nice Cedex 2, France
¹⁹ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
²⁰ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
²¹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
²² Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
²³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²⁴ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
²⁵ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
²⁶ Institut de Ciencies de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
²⁷ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
²⁸ Admatis, 5. Kandó Kálmán Street, 3534 Miskolc, Hungary
²⁹ Depto. de Astrofisica, Centro de Astrobiología (CSIC-INTA), ESAC campus, 28692 Villanueva de la Canada, Madrid, Spain
³⁰ Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, P-333, MS-16, Cambridge, MA 02138, USA
³² Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³³ NASA, Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
³⁴ Université de Paris, Institut de physique du globe de Paris, CNRS, 75005 Paris, France
³⁵ Centre for Mathematical Sciences Lund University, Box 118, SE 221 00 Lund, Sweden
³⁶ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
³⁷ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
³⁸ University of California at Santa Cruz, Santa Cruz, CA, USA
³⁹ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁴⁰ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁴¹ Astronomical Institute, Slovak Academy of Science, Stellar Department, Tatranská Lomnica, 05960 Vysoké Tatry, Slovakia
⁴² ELTE Eötvös Lorând University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁴³ MTA-ELTE Exoplanet Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁴⁴ MTA-ELTE Lendület Milky Way Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁴⁵ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁴⁶ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁴⁷ Observatoire de Haute-Provence, CNRS, Université d’Aix-Marseille, 04870 Saint-Michel-l’Observatoire, France
⁴⁸ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁴⁹ Science and Operations Department – Science Division (SCI-SC), Directorate of Science, European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201-AZ Noordwijk, The Netherlands
⁵⁰ NASA Ames Research Center, Mail Stop 269-3, Bldg. T35A, Rm. 102, PO Box 1, Moffett Field, CA 94035-0001, USA
⁵¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
⁵² IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
⁵³ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵⁴ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁵⁵ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵⁶ Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna, Austria
⁵⁷ INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁵⁸ Citizen Scientist, Marica, Rio de Janeiro, Brazil
⁵⁹ Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
⁶⁰ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universita degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁶¹ ETH Zurich, Department of Physics, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁶² Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
⁶³ ESTEC, European Space Agency, 2201 AZ Noordwijk, The Netherlands
⁶⁴ Center for Astronomy and Astrophysics, Technical University Berlin, Hardenberstrasse 36, 10623 Berlin, Germany
⁶⁵ Institut für Geologische Wissenschaften, Freie Universität Berlin, 12249 Berlin, Germany
⁶⁶ Royal Astronomical Society, Burlington House, Piccadilly, London W1J 0BQ, UK
⁶⁷ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁶⁸ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
⁶⁹ SETI Institute/NASA Ames Research Center, 339 Bernardo Ave, Suite 200, Mountain View, CA 94043, US
⁷⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 12 January 2022
Accepted: 19 June 2022

Abstract

We present the discovery of two small planets transiting HD 93963A (TOI-1797), a GOV star (M_* = 1.109 ± 0.043M_⊙, R_* = 1.043 ± 0.009 R_⊙) in a visual binary system. We combined TESS and CHEOPS space-borne photometry with MuSCAT 2 ground-based photometry, ‘Alopeke and PHARO high-resolution imaging, TRES and FIES reconnaissance spectroscopy, and SOPHIE radial velocity measurements. We validated and spectroscopically confirmed the outer transiting planet HD 93963 A c, a sub-Neptune with an orbital period of P_c ≈ 3.65 d that was reported to be a TESS object of interest (TOI) shortly after the release of Sector 22 data. HD 93963 A c has amass of M_c = 19.2 ± 4.1 M_⊕ and a radius of R_c = 3.228 ± 0.059 R_⊕, implying a mean density of ρ_c = 3.1 ± 0.7 g cm^-3. The inner object, HD 93963 A b, is a validated 1.04 d ultra-short period (USP) transiting super-Earth that we discovered in the TESS light curve and that was not listed as a TOI, owing to the low significance of its signal (TESS signal-to-noise ratio ≈6.7, TESS + CHEOPS combined transit depth D_b = 141.5_−8.3^+8.5 ppm). We intensively monitored the star with CHEOPS by performing nine transit observations to confirm the presence of the inner planet and validate the system. HD 93963 A b is the first small (R_b = 1.35 ± 0.042 R_⊕) USP planet discovered and validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is not significantly detected in our radial velocities (M_b = 7.8 ± 3.2 M_⊕). The two planets are on either side of the radius valley, implying that they could have undergone completely different evolution processes. We also discovered a linear trend in our Doppler measurements, suggesting the possible presence of a long-period outer planet. With a V-band magnitude of 9.2, HD 93963 A is among the brightest stars known to host a USP planet, making it one of the most favourable targets for precise mass measurement via Doppler spectroscopy and an important laboratory to test formation, evolution, and migration models of planetary systems hosting ultra-short period planets.