The changing face of AU Mic b: Stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
Journal article, 2021
AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey from the ground. The refined orbital period of AU Mic b is 8.462995 ± 0.000003 d, whereas the stellar rotational period is Prot = 4.8367 ± 0.0006 d. The two periods indicate a 7:4 spin-orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 min. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 min. We find that the outer companion, AU Mic c, may cause the observed TTVs.
Planetary systems
Author
G.M. Szabó
Eötvös Loránd University (ELTE)
D. Gandolfi
Istituto nazionale di astrofisica (INAF)
A. Brandeker
Stockholm University
Szilard Csizmadia
German Aerospace Center (DLR)
Z. Garai
Slovak Academy of Sciences
Eötvös Loránd University (ELTE)
N. Billot
University of Geneva
C. Broeg
University of Bern
D. Ehrenreich
University of Geneva
A. Fortier
University of Bern
L. Fossati
Institut fur Weltraumforschung
S. Hoyer
Laboratoire d'Astrophysique de Marseille
L. Kiss
The University of Sydney
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
A. L. des Etangs
Institut d 'Astrophysique de Paris
P. Maxted
Keele University
I. Ribas
Institute of Space Studies of Catalonia (IEEC)
Institute of Space Sciences (ICE) - CSIC
Y. Alibert
University of Bern
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
G. A. Escudé
Institute of Space Sciences (ICE) - CSIC
Institute of Space Studies of Catalonia (IEEC)
T. Bárczy
Admatis
S.C.C. Barros
University of Porto
D. Barrado
Centro de Astrobiologia (CAB)
W. Baumjohann
Institut fur Weltraumforschung
M. Beck
University of Geneva
T. Beck
University of Bern
A. Bekkelien
University of Geneva
X. Bonfils
Grenoble Alpes University
W. Benz
University of Bern
L. Borsato
Istituto nazionale di astrofisica (INAF)
M.-D. Busch
University of Bern
J. Cabrera
German Aerospace Center (DLR)
S. Charnoz
Institut de Physique du Globe de Paris
A. Collier Cameron
University of St Andrews
C. Corral Van Damme
European Space Research and Technology Centre (ESA ESTEC)
M. B. Davies
Lund University
L. Delrez
University of Liège
M. Deleuil
Laboratoire d'Astrophysique de Marseille
O. Demangeon
Laboratoire d'Astrophysique de Marseille
University of Porto
B.O. Demory
University of Bern
Anders Erikson
German Aerospace Center (DLR)
Malcolm Fridlund
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Leiden University
D. Futyan
University of Geneva
A. Garciá Muñoz
Technische Universität Berlin
Michaël Gillon
University of Liège
M. Guedel
University of Vienna
P. Guterman
Institut National des Sciences de l'Univers
Laboratoire d'Astrophysique de Marseille
Kevin Heng
University of Bern
The University of Warwick
K. Isaak
European Space Research and Technology Centre (ESA ESTEC)
G. Lacedelli
University of Padua
Istituto nazionale di astrofisica (INAF)
J. Laskar
Paris Observatory
M. Lendl
University of Geneva
C. Lovis
University of Geneva
A. Luntzer
University of Vienna
D. Magrin
Istituto nazionale di astrofisica (INAF)
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholm University
H. P. Osborn
University of Bern
Massachusetts Institute of Technology (MIT)
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
University of Padua
Istituto nazionale di astrofisica (INAF)
Don L. Pollacco
The University of Warwick
D. Queloz
University of Cambridge
University of Geneva
Roberto Ragazzoni
Istituto nazionale di astrofisica (INAF)
University of Padua
N. Rando
European Space Research and Technology Centre (ESA ESTEC)
H. Rauer
Technische Universität Berlin
Freie Universität Berlin
German Aerospace Center (DLR)
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
L. M. Serrano
University of Turin
D. Sicilia
Istituto nazionale di astrofisica (INAF)
A.E. Simon
University of Bern
Alexis M. S. Smith
German Aerospace Center (DLR)
S.G. Sousa
University of Porto
Manfred B. Steller
Institut fur Weltraumforschung
Nicolas Thomas
University of Bern
S. Udry
University of Geneva
V. Van Grootel
University of Liège
N. A. Walton
University of Cambridge
T.G. Wilson
University of St Andrews
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 654 A159Subject Categories
Astronomy, Astrophysics and Cosmology
Other Physics Topics
Condensed Matter Physics
DOI
10.1051/0004-6361/202140345