HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

ABSTRACT We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast }$: 0.99 $\text{M}_{\odot }$; $R_{\ast }$: 1.13 $\text{R}_{\odot }$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 d and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b’s mass to $6.0^{+1.5}_{-1.6}$ $\text{M}_{\rm{\oplus }}$ and $8.5^{+1.3}_{-1.4}$ $\text{M}_{\rm{\oplus }}$, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 $\text{M}_{\rm{\oplus }}$ and orbital periods of 35.7 and 89 d. Additionally, we reject the initial hypothesis that the 35.7-d periodic signal was due to stellar activity. We also determine HD 85426 b’s radius to be $2.78^{+0.05}_{-0.04}$ $\text{R}_{\rm{\oplus }}$ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-11-11
DOI
https://doi.org/10.1093/mnras/staf1934
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
0.00

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article

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

José Ángel Cabrera, Ken Rice, T. Bárczy, A. Collier Cameron et al.
Monthly Notices of the Royal Astronomical Society
Stellar, planetary, and galactic studies
article

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

José Ángel Cabrera, Ken Rice, T. Bárczy, A. Collier Cameron, N. Billot, H. Rauer, Y. Alibert, A. M. S. Smith, J. Laskar, W. Benz, Maximilian N. Günther, Simon L. Grimm, S. Sulis, L. Malavolta, Annelies Mortier, L. Borsato, M. Gillon, P. F. L. Maxted, D. Pollacco, A. Anna John, Soléne Ulmer-Moll, John Jenkins, V. Nascimbeni, H. P. Osborn, M. Lendl, Ε. Πάλλη, L. L. Kiss, David W. Latham, D. Gandolfi, D. Queloz, A. C. M. Correia, C. Mordasini, A. E. Simon, G. Piotto, M. B. Davies, T. Zingales, Karen A. Collins, M Stalport, J. A. Egger, R. Alonso, Alessandro Sozzetti, G. Peter, A. F. Martínez Fiorenzano, Roberto Ragazzoni, X Dumusque, J. Korth, Federica Rescigno, Florian Lienhard, A. Fortier, A. Derekas, Luca Naponiello, Lars A. Buchhave, I. Ribas, K. W. F. Lam, K. G. Isaak, Ch. Helling, M. Cretignier, C. Broeg, A. Heitzmann, G. Scandariato, M Fridlund, D. Barrado, N. A. Walton, A. Lecavelier des Étangs, Szilárd Csizmadia, W. Baumjohann, S. C. C. Barros, E. Villaver, N. C. Santos, Patricio E. Cubillos, R. D. Haywood, Demetrio Magrin, Ben S Lakeland, K. Gazeas, J. Venturini, G. Olofsson, Brice-Olivier Demory, M Deleuil, Adrien Leleu, L. Fossati, D. Ehrenreich, A. Deline, B Edwards, A. Brandeker, T. G. Wilson, S. Udry, B. Merín, Larissa Palethorpe, V. Van Grootel, S. G. Sousa, N. Rando, D. Piazza, O. D. S. Demangeon, D Ségransan, Gy. M. Szabó, Anders Erikson, M. Güdel, I. Pagano, R. Ottensamer
article en

Abstract

ABSTRACT We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast }$: 0.99 $\text{M}_{\odot }$; $R_{\ast }$: 1.13 $\text{R}_{\odot }$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 d and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b’s mass to $6.0^{+1.5}_{-1.6}$ $\text{M}_{\rm{\oplus }}$ and $8.5^{+1.3}_{-1.4}$ $\text{M}_{\rm{\oplus }}$, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 $\text{M}_{\rm{\oplus }}$ and orbital periods of 35.7 and 89 d. Additionally, we reject the initial hypothesis that the 35.7-d periodic signal was due to stellar activity. We also determine HD 85426 b’s radius to be $2.78^{+0.05}_{-0.04}$ $\text{R}_{\rm{\oplus }}$ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.

Monthly Notices of the Royal Astronomical SocietyVol. 545(3)
Eötvös Loránd University (HU), University of Geneva (CH), University of Bern (CH), Leiden University (NL), Ames Research Center (US), Centre National de la Recherche Scientifique (FR), University of Vienna (AT), Institute of Space Sciences (ES), Austrian Academy of Sciences (AT), University of Padua (IT), University of Liège (BE), Universidad de La Laguna (ES), Stockholm University (SE), University of St Andrews (GB), Universidade do Porto (PT), Lund University (SE), ZHAW Zurich University of Applied Sciences (CH), National and Kapodistrian University of Athens (GR), University of Zurich (CH), University of Applied Sciences Leiden (NL), Aix-Marseille Université (FR), University of Exeter (GB), University of Cambridge (GB), Université Paris Sciences et Lettres (FR), Institut d'Astrophysique de Paris (FR), European Space Agency (FR), Konkoly Observatory (HU), Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR) (DE), ETH Zurich (CH), University of Warwick (GB), Sorbonne Université (FR), University of Oxford (GB), Graz University of Technology (AT), Institute of Astrophysics and Space Sciences (PT), Space Research Institute (AT), Institut d'Estudis Espacials de Catalunya (ES), European Space Astronomy Centre (ES), Laboratoire d’Astrophysique de Marseille (FR), Institute of Particle Physics (CA), Osservatorio Astrofisico di Torino (IT), Cavendish Hospital (GB), Instituto de Física Teórica (ES), Institute of Astronomy (RU), Osservatorio Astrofisico di Catania (IT), FZU ‒ Institute of Physics of the Academy of Sciences of the Czech Republic (CZ), Center for Astrophysics Harvard & Smithsonian (US), Centro de Astrobiología (ES), Instituto de Astrofísica de Canarias (ES), AlbaNova (SE), Computational Physics (United States) (US), Astronomy and Space (AU), Osservatorio Astronomico di Padova (IT), Telescopio Nazionale Galileo (ES), Leiden Observatory, European Space Research and Technology Centre (NL), Space Research Organisation Netherlands (NL), UK Astronomy Technology Centre (GB), Institut de Mécanique Céleste et de Calcul des Éphémérides (FR), University of Turin (IT), Keele University (GB), Chalmers University of Technology (SE), Freie Universität Berlin (DE), University of Coimbra (PT), University of Birmingham (GB), International Space Science Institute (CH), Technical University of Denmark (DK), University of Edinburgh (GB)
National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, Nvidia, UK Space Agency, Space Telescope Science Institute, UK Research and Innovation, Dipartimenti di Eccellenza, European Space Agency, University of Warwick, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Université de Genève, Ames Research Center, Science Mission Directorate, Science and Technology Facilities Council
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