TOI-5678b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
Journal article, 2023
Context. A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events. Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates. Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements. Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2σ. The planet TOI-5678 b has a mass of 20 ± 4 Earth masses (M) and a radius of 4.91 ± 0.08 R Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2±1.7-1.3 M. Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 S). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.
Planets and satellites: gaseous planets
Planets and satellites: detection
Methods: data analysis
Planets and satellites: individual: TOI-5678
Author
S. Ulmer-Moll
University of Geneva
University of Bern
H. P. Osborn
Massachusetts Institute of Technology (MIT)
University of Bern
A. Tuson
University of Cambridge
J. A. Egger
University of Bern
M. Lendl
University of Geneva
P. Maxted
Keele University
A. Bekkelien
University of Geneva
A.E. Simon
University of Bern
G. Olofsson
Stockholm University
V. Adibekyan
University of Porto
Y. Alibert
University of Bern
A. Bonfanti
Institut fur Weltraumforschung
F. Bouchy
University of Geneva
A. Brandeker
Stockholm University
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
D. Gandolfi
University of Turin
C. Mordasini
University of Bern
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
S. Salmon
University of Geneva
L. M. Serrano
University of Turin
S. G. Sousa
University of Porto
T.G. Wilson
University of St Andrews
M. Rieder
University of Bern
J. Hasiba
Institut fur Weltraumforschung
J. Asquier
European Space Agency (ESA)
D. Sicilia
Istituto nazionale di astrofisica (INAF)
I. Walter
German Aerospace Center (DLR)
R. Alonso
Instituto de Astrofísica de Canarias
University of La Laguna
G. Anglada
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
Spanish National Research Council (CSIC)
D. Barrado
European Space Agency (ESA)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
M. Beck
University of Geneva
T. Beck
University of Bern
W. Benz
University of Bern
N. Billot
University of Geneva
X. Bonfils
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
University of Bern
T. Bárczy
Admatis
J. Cabrera
German Aerospace Center (DLR)
S. Charnoz
Institut de Physique du Globe de Paris
M. Cointepas
University of Geneva
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)
A. Collier Cameron
University of St Andrews
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
A. Deline
University of Geneva
L. Delrez
University of Liège
O. Demangeon
University of Porto
B.O. Demory
University of Bern
X. Dumusque
University of Geneva
D. Ehrenreich
University of Geneva
N. L. Eisner
Flatiron Institute
Anders Erikson
German Aerospace Center (DLR)
A. Fortier
University of Bern
L. Fossati
Institut fur Weltraumforschung
Michaël Gillon
University of Liège
N. Grieves
University of Geneva
M. Gudel
University of Vienna
J. Hagelberg
University of Geneva
R. Helled
University of Zürich
S. Hoyer
Laboratoire d'Astrophysique de Marseille
K. Isaak
European Space Agency (ESA)
L. Kiss
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
C. Lovis
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
J. F. Otegi
University of Geneva
R. Ottensammer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
E. Palle
Instituto de Astrofísica de Canarias
G. Peter
German Aerospace Center (DLR)
Giampaolo P. Piotto
University of Padua
Istituto nazionale di astrofisica (INAF)
Don L. Pollacco
The University of Warwick
A. Psaridi
University of Geneva
D. Queloz
Swiss Federal Institute of Technology in Zürich (ETH)
University of Cambridge
Roberto Ragazzoni
Istituto nazionale di astrofisica (INAF)
University of Padua
N. Rando
European Space Agency (ESA)
H. Rauer
German Aerospace Center (DLR)
Technische Universität Berlin
I. Ribas
Spanish National Research Council (CSIC)
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
A. M.S. Smith
German Aerospace Center (DLR)
Manfred B. Steller
Institut fur Weltraumforschung
G.M. Szabó
Eötvös Loránd University (ELTE)
D. Segransan
University of Geneva
Nicolas Thomas
University of Bern
S. Udry
University of Geneva
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
N. A. Walton
University of Cambridge
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 674 A43Exoplanet diversity with satellite studies
Swedish National Space Board (174/18), 2019-02-04 -- 2023-08-01.
Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Other Physics Topics
DOI
10.1051/0004-6361/202245478