Transit-timing variations in the AU Mic system observed with CHEOPS
Journal article, 2025
Context. AU Mic is a very active M dwarf star with an edge-on debris disk and two known transiting sub-Neptunes with a possible third planetary companion. The two transiting planets exhibit significant transit-timing variations (TTVs) that are caused by the gravi tational interaction between the bodies in the system. Aims. Using photometrical observations taken with the CHaracterizing ExOPlanet Satellite (CHEOPS), we aim to constrain the plan etary radii, the orbital distances, and the periods of AU Mic b and c. Furthermore, our goal is to determine the superperiod of the TTVs for AU Mic b and to update the transit ephemeris for both planets. Additionally, based on the perceived TTVs, we study the possible presence of a third planet in the system. Methods. We conducted ultra-high precision photometric observations with CHEOPS in 2022 and 2023. We used Allesfitter to fit the planetary transits and to constrain the planetary and orbital parameters. We combined our new measurements with results from previous years to determine the periods and amplitudes of the TTVs. We applied dynamical modelling based on TTV measurements from the 2018-2023 period to reconstruct the perceived variations. Results. We found that the orbital distances and periods for AU Mic b and c agree with the results from previous works. However, the values for the planetary radii deviate slightly from previous values, which we attribute to the effect of spots on the stellar surface. AU Mic c showed very strong TTVs, with transits that occurred ∼80 minutes later in 2023 than in 2021. Through a dynamical analysis of the system, we found that the observed TTVs can be explained by a third planet with an orbital period of ∼12.6 days and a mass of 0.2030.024+0.022 MO. We explored the orbital geometry of the system and found that AU Mic c has a misaligned retrograde orbit. The limited number of AU Mic observations prevented us from determining the exact dynamical configuration and planetary parameters. Further monitoring of the system with CHEOPS might help to improve these results.
Planets and satellites: fundamental parameters
Author
Boldog
Eötvös Loránd University (ELTE)
Research Centre For Astronomy and Earth Sciences
Hungarian Academy of Sciences
G.M. Szabó
Eötvös Loránd University (ELTE)
L. Kriskovics
Research Centre For Astronomy and Earth Sciences
Hungarian Academy of Sciences
L. Borsato
Istituto nazionale di astrofisica (INAF)
D. Gandolfi
University of Turin
M. Lendl
University of Geneva
Maximilian N. Günther
European Space Agency (ESA)
A. Heitzmann
University of Geneva
T.G. Wilson
The University of Warwick
A. Brandeker
Stockholm University
Z. Garai
Eötvös Loránd University (ELTE)
Slovak Academy of Sciences
Y. Alibert
Physics Institute
University of Bern
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
T. Bárczy
Admatis
D. Barrado Navascues
Centro de Astrobiologia (CAB)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
W. Benz
University of Bern
Physics Institute
N. Billot
University of Geneva
C. Broeg
Physics Institute
University of Bern
A. Collier Cameron
University of St Andrews
A. Correia
University of Coimbra
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
O. Demangeon
University of Porto
B.O. Demory
Physics Institute
University of Bern
A. Derekas
Eötvös Loránd University (ELTE)
Billy Edwards
Netherlands Institute for Space Research (SRON)
J. A. Egger
Physics Institute
D. Ehrenreich
University of Geneva
Anders Erikson
German Aerospace Center (DLR)
A. Fortier
Physics Institute
University of Bern
L. Fossati
Institut fur Weltraumforschung
Malcolm Fridlund
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Leiden University
K. Gazeas
University of Athens
Michaël Gillon
University of Liège
M. Gudel
University of Vienna
P. Guterman
CS20330
Laboratoire d'Astrophysique de Marseille
Ch. Helling
Technische Universität Graz
Institut fur Weltraumforschung
K. Isaak
European Space Agency (ESA)
L. L. Kiss
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
E. Kopp
German Aerospace Center (DLR)
Judith Korth
Lund University
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
A. Luntzer
University of Vienna
D. Magrin
Istituto nazionale di astrofisica (INAF)
G. Mantovan
University of Padua
L. Marafatto
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
Bruno Merín
European Space Agency (ESA)
C. Mordasini
University of Bern
Physics Institute
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
Instituto de Astrofísica de Canarias
University of La Laguna
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
K. Poppenhaeger
Leibniz Association
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
Freie Universität Berlin
German Aerospace Center (DLR)
I. Ribas
Spanish National Research Council (CSIC)
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
M. Rieder
University of Bern
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
A.E. Simon
University of Bern
Physics Institute
A. M.S. Smith
German Aerospace Center (DLR)
S.G. Sousa
University of Porto
R. Southworth
European Space Agency (ESA)
M. Stalport
University of Liège
S. Sulis
Laboratoire d'Astrophysique de Marseille
S. Udry
University of Geneva
S. Ulmer-Moll
University of Geneva
Physics Institute
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
Istituto nazionale di astrofisica (INAF)
University of Padua
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 694 A137Exoplanet diversity with satellite studies
Swedish National Space Board (174/18), 2019-02-04 -- 2023-08-01.
Exoplanets from space – CHEOPS and PLATO, ESA’s next two projects
Swedish National Space Board (174/18), 2017-01-01 -- 2022-12-31.
Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202452699