Letter to the Editor

TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS^{⋆,⋆⋆,⋆⋆⋆}

¹ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
e-mail: andrea.bonfanti@oeaw.ac.at
² Dipartimento di Fisica, Universita degli Studi di Torino, Via Pietro Giuria 1 10125 Torino, Italy
³ Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁴ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
⁵ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁶ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁷ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
⁸ Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁹ Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹⁰ Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
¹¹ Sub-department of Astrophysics, Department of Physics, University of Oxford, Oxford OX1 3RH, UK
¹² Astrobiology Research Unit, Université, de Liège Allée du 6 Août 19C, 4000 Liège, Belgium
¹³ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
¹⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁵ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile
¹⁸ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
¹⁹ Departamento de Astrofisica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
²⁰ Institut de Ciencies de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
²¹ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
²² Admatis, 5. Kandó Kálmán Street, 3534 Miskolc, Hungary
²³ Depto. de Astrofisica, Centro de Astrobiologia (CSIC-INTA), ESAC campus, 28692 Villanueva de la Cañada, (Madrid), Spain
²⁴ Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA
²⁵ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
²⁶ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁷ Center for Space and Habitability, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
²⁸ Université de Paris, Institut de physique du globe de Paris, CNRS, 75005 Paris, France
²⁹ ESTEC, European Space Agency, 2201 AZ Noordwijk, The Netherlands
³⁰ INAF, Osservatorio Astrofisico di Torino, Via Osservatorio, 20, 10025 Pino Torinese, To, Italy
³¹ Centre for Mathematical Sciences, Lund University, Box 118, 221 00 Lund, Sweden
³² Aix Marseille Univ, CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France
³³ Centre Vie dans l’Univers, Faculté des sciences, Université de Genève, Quai Ernest-Ansermet 30, 1211 Genève 4, Switzerland
³⁴ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
³⁵ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
³⁶ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
³⁷ 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 Noordwijk, The Netherlands
³⁸ Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna, Austria
³⁹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklás út 15-17, Hungary
⁴⁰ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁴¹ IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
⁴² Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis blvd. Arago, 75014 Paris, France
⁴³ Laboratório Nacional de Astrofísica, Rua Estados Unidos 154, 37504-364 Itajubá, MG, Brazil
⁴⁴ Universidade de São Paulo, IAG, Departamento de Astronomia, Rua do Matão 1226, 05509-900 São Paulo, SP, Brazil
⁴⁵ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁴⁶ Physikalisches Institut, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁴⁷ INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁴⁸ Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
⁴⁹ Dipartimento di Fisica e Astronomia "Galileo Galilei", Universita degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁵⁰ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵¹ ETH Zurich, Department of Physics, Wolfgang-Pauli-Strasse 2, 8093 Zurich, Switzerland
⁵² Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
⁵³ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
⁵⁴ Institut für Geologische Wissenschaften, Freie Universität Berlin, 12249 Berlin, Germany
⁵⁵ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁵⁶ MTA-ELTE Exoplanet Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁵⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 2 December 2022
Accepted: 21 February 2023

Abstract

Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ.

Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope.

Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series.

Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of M_b = 20.4_−2.5^+2.6 M_⊕ (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of R_b = 3.490_−0.064^+0.070 R_⊕ (∼1.9%). Our mass and radius measurements imply a mean density of ρ_b = 2.65_−0.35^+0.37 g cm⁻³ (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41_−0.20^+0.34 M_⊕ and a thickness of 1.05_−0.29^+0.30 R_⊕.

Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b.