HARPS-N, TESS, and CHEOPSā discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426
Journal article, 2026
We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star (: 0.99;: 1.13; 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 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 and, 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 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 and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.
techniques: radial velocities
stars: individual (HD 85426)
techniques: spectroscopic
planets and satellites: fundamental parameters
planets and satellites: composition
techniques: photometric
Author
F. Lienhard
Swiss Federal Institute of Technology in Zürich (ETH)
A. Mortier
University of Birmingham
A. Collier Cameron
University of St Andrews
M. Cretignier
University of Oxford
L. Borsato
Istituto nazionale di astrofisica (INAF)
A. Anna John
University of Birmingham
University of St Andrews
J. A. Egger
Physics Institute
M. Stalport
University of Liège
T.G. Wilson
The University of Warwick
A. Deline
University of Geneva
A. Fortier
Physics Institute
University of Bern
D. W. Latham
Harvard-Smithsonian Center for Astrophysics
L. Malavolta
University of Padua
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
S.G. Sousa
University of Porto
S. L. Grimm
University of Zürich
Swiss Federal Institute of Technology in Zürich (ETH)
L. A. Buchhave
Technical University of Denmark (DTU)
Y. Alibert
University of Bern
Physics Institute
B. S. Lakeland
University of Exeter
University of Birmingham
X. Dumusque
University of Geneva
J. Cabrera
German Aerospace Center (DLR)
L. Naponiello
Istituto nazionale di astrofisica (INAF)
A. Correia
University of Coimbra
F. Rescigno
University of Exeter
University of Birmingham
L. Fossati
Institut fur Weltraumforschung
A. Sozzetti
Istituto nazionale di astrofisica (INAF)
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
T. Bárczy
Admatis
D. Barrado
European Space Agency (ESA)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
W. Benz
Physics Institute
University of Bern
N. Billot
University of Geneva
A. Brandeker
Stockholm University
C. Broeg
University of Bern
Physics Institute
Karen A. Collins
Harvard-Smithsonian Center for Astrophysics
Szilard Csizmadia
German Aerospace Center (DLR)
P. E. Cubillos
Istituto nazionale di astrofisica (INAF)
Institut fur Weltraumforschung
Melvyn B. Davies
Lund University
M. Deleuil
Laboratoire d'Astrophysique de Marseille
O. Demangeon
University of Porto
B.O. Demory
University of Bern
Physics Institute
A. Derekas
Eötvös Loránd University (ELTE)
Billy Edwards
Netherlands Institute for Space Research (SRON)
D. Ehrenreich
University of Geneva
Anders Erikson
German Aerospace Center (DLR)
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
D. Gandolfi
University of Turin
K. Gazeas
University of Athens
Michaël Gillon
University of Liège
M. Gudel
University of Vienna
Maximilian N. Günther
European Space Agency (ESA)
R. D. Haywood
University of Exeter
A. Heitzmann
University of Geneva
Ch. Helling
Technische Universität Graz
Institut fur Weltraumforschung
K. Isaak
European Space Agency (ESA)
Jon M. Jenkins
National Aeronautics and Space Administration (NASA)
L. L. Kiss
Hungarian Academy of Sciences
Eötvös Loránd University (ELTE)
Judith Korth
University of Geneva
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
A. Leleu
University of Geneva
Physics Institute
M. Lendl
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
A. F.Martínez Fiorenzano
Istituto nazionale di astrofisica (INAF)
Bruno Merín
European Space Agency (ESA)
C. Mordasini
Physics Institute
University of Bern
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholm University
H. P. Osborn
Swiss Federal Institute of Technology in Zürich (ETH)
University of Bern
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
L. Palethorpe
University of Edinburgh
Enric Palle
University of La Laguna
Instituto de Astrofísica de Canarias
G. Peter
German Aerospace Center (DLR)
D. Piazza
University of Bern
Giampaolo P. Piotto
Istituto nazionale di astrofisica (INAF)
University of Padua
Don L. Pollacco
The University of Warwick
D. Queloz
University of Cambridge
Swiss Federal Institute of Technology in Zürich (ETH)
Roberto Ragazzoni
University of Padua
Istituto nazionale di astrofisica (INAF)
N. Rando
European Space Agency (ESA)
H. Rauer
German Aerospace Center (DLR)
Freie Universität Berlin
I. Ribas
Spanish National Research Council (CSIC)
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
K. Rice
University of Edinburgh
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
A.E. Simon
Physics Institute
University of Bern
A. M.S. Smith
German Aerospace Center (DLR)
S. Sulis
Laboratoire d'Astrophysique de Marseille
G.M. Szabó
Hungarian Research Network
Eötvös Loránd University (ELTE)
S. Udry
University of Geneva
S. Ulmer-Moll
Leiden University
University of Liège
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
E. Villaver
University of La Laguna
Instituto de Astrofísica de Canarias
N. A. Walton
University of Cambridge
Tiziano Zingales
University of Padua
Istituto nazionale di astrofisica (INAF)
Monthly Notices of the Royal Astronomical Society
00358711 (ISSN) 13652966 (eISSN)
Vol. 545 3 staf1934Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1093/mnras/staf1934