The CHEOPS view of HD 95338b: Refined transit parameters, and a search for exomoons
Journal article, 2025
Context. Despite the ever-increasing number of known exoplanets, no uncontested detections have been made of their satellites, known as exomoons. Aims. The quest to find exomoons is at the forefront of exoplanetary sciences. Certain space-born instruments are thought to be suitable for this purpose. We show the progress made with the CHaracterising ExOPlanets Satellite (CHEOPS) in this field using the HD 95338 planetary system. We present a novel methodology as an important step in the quest to find exomoons. Methods. We utilised ground-based spectroscopic data in combination with Gaia observations to obtain precise stellar parameters. These were then used as input in the analysis of the planetary transits observed by CHEOPS and the Transiting Exoplanet Survey Satellite (TESS). In addition, we searched for the signs of satellites primarily in the form of additional transits in the Hill sphere of the eccentric Neptune-sized planet HD 95338b in a sequential approach based on four CHEOPS visits. We also briefly explored the transit timing variations of the planet. Results. We present refined stellar and planetary parameters, narrowing down the uncertainty on the planet-to-star radius ratio by a factor of ten. We also pin down the ephemeris of HD 95338b. Using injection-and-retrieval tests, we show that a 5σ detection of an exomoon would be possible at RMoon = 0.8 R⊗ with the methodology presented here. Conclusions. We exclude the transit of an exomoon in the HD 95338 system with RMoon ≈ 0.6 R⊗ at the 1σ level. The algorithm used for finding the transit-like event can be used as a baseline for other similar targets, observed by CHEOPS or other missions.
Methods: data analysis
Planets and satellites: individual: HD 95338b
Techniques: photometric
Author
Sz Kálmán
Research Centre for Astronomy and Earth Sciences
Hungarian Academy of Sciences
Eötvös Loránd University (ELTE)
A.E. Simon
University of Bern
A. Deline
University of Geneva
Szilard Csizmadia
German Aerospace Center (DLR)
G.M. Szabó
Eötvös Loránd University (ELTE)
D. Ehrenreich
University of Geneva
T.G. Wilson
The University of Warwick
Maximilian N. Günther
European Space Agency (ESA)
A. Heitzmann
University of Geneva
S.G. Sousa
University of Porto
M. Farnir
University of Liège
A. Bonfanti
Institut fur Weltraumforschung
A. M.S. Smith
German Aerospace Center (DLR)
A. Pál
Hungarian Academy of Sciences
Eötvös Loránd University (ELTE)
Research Centre for Astronomy and Earth Sciences
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
V. Adibekyan
University of Porto
A. Brandeker
Stockholm University
S. Charnoz
Institut de Physique du Globe de Paris
B. Akinsanmi
University of Geneva
S.C.C. Barros
University of Porto
X. Song
Beijing University of Technology
University of Geneva
Y. Alibert
Eötvös Loránd University (ELTE)
University of Bern
R. Alonso
Instituto de Astrofísica de Canarias
University of La Laguna
T. Bárczy
Admatis
D. Barrado Navascues
European Space Agency (ESA)
W. Baumjohann
Institut fur Weltraumforschung
W. Benz
Eötvös Loránd University (ELTE)
University of Bern
N. Billot
University of Geneva
F. Biondi
Max Planck Society
Istituto nazionale di astrofisica (INAF)
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
Eötvös Loránd University (ELTE)
University of Bern
A. Collier Cameron
University of St Andrews
C. Corral Van Damme
European Space Agency (ESA)
A. Correia
University of Coimbra
P. E. Cubillos
Institut fur Weltraumforschung
Istituto nazionale di astrofisica (INAF)
Melvyn B. Davies
Lund University
M. Deleuil
Laboratoire d'Astrophysique de Marseille
O. Demangeon
University of Porto
B.O. Demory
Eötvös Loránd University (ELTE)
University of Bern
A. Derekas
Eötvös Loránd University (ELTE)
Billy Edwards
Netherlands Institute for Space Research (SRON)
J. A. Egger
Eötvös Loránd University (ELTE)
Anders Erikson
German Aerospace Center (DLR)
A. Fortier
Eötvös Loránd University (ELTE)
University of Bern
L. Fossati
Institut fur Weltraumforschung
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
P. Guterman
Laboratoire d'Astrophysique de Marseille
Division Technique INSU
J. Hasiba
Institut fur Weltraumforschung
Ch. Helling
Technische Universität Graz
Institut fur Weltraumforschung
K. Isaak
European Space Agency (ESA)
L. L. Kiss
Eötvös Loránd University (ELTE)
Research Centre for Astronomy and Earth Sciences
Hungarian Academy of Sciences
Judith Korth
University of Geneva
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
A. Lecavelier des Etangs
Centre national de la recherche scientifique (CNRS)
A. Leleu
Eötvös Loránd University (ELTE)
University of Geneva
M. Lendl
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
Bruno Merín
European Space Agency (ESA)
C. Mordasini
Eötvös Loránd University (ELTE)
M. Munari
Istituto nazionale di astrofisica (INAF)
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholm University
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
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
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 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)
N. C. Santos
University of Porto
D. Segransan
University of Geneva
M. Stalport
University of Liège
S. Sulis
Laboratoire d'Astrophysique de Marseille
S. Udry
University of Geneva
B. Ulmer
University of Bern
S. Ulmer-Moll
University of Liège
Eötvös Loránd University (ELTE)
University of Geneva
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
E. Villaver
Instituto de Astrofísica de Canarias
University of La Laguna
N. A. Walton
University of Cambridge
S. Wolf
University of Bern
Tiziano Zingales
University of Padua
Istituto nazionale di astrofisica (INAF)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 701 A240Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202554040