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

Planets and satellites: individual: TOI-5678

Methods: data analysis

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 Research and Technology Centre (ESA ESTEC)

D. Sicilia

Istituto nazionale di astrofisica (INAF)

I. Walter

German Aerospace Center (DLR)

R. Alonso

University of La Laguna

Instituto de Astrofísica de Canarias

G. Anglada

Institute of Space Sciences (ICE) - CSIC

Institute of Space Studies of Catalonia (IEEC)

D. Barrado

European Space Astronomy Centre (ESAC)

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

Institut fur Weltraumforschung

Istituto nazionale di astrofisica (INAF)

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 Research and Technology Centre (ESA ESTEC)

L. Kiss

Hungarian Academy of Sciences

Eötvös Loránd University (ELTE)

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

Istituto nazionale di astrofisica (INAF)

University of Padua

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

University of Padua

Istituto nazionale di astrofisica (INAF)

N. Rando

European Space Research and Technology Centre (ESA ESTEC)

H. Rauer

Technische Universität Berlin

German Aerospace Center (DLR)

I. Ribas

Institute of Space Sciences (ICE) - CSIC

Institute of Space Studies of Catalonia (IEEC)

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 A43

Exoplanet diversity with satellite studies

Swedish National Space Board (174/18), 2019-02-04 -- 2023-08-01.

Subject Categories

Astronomy, Astrophysics and Cosmology

Other Physics Topics

DOI

10.1051/0004-6361/202245478

More information

Latest update

9/15/2023