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
D. Gandolfi
A. Brandeker
Szilard Csizmadia
Z. Garai
N. Billot
C. Broeg
D. Ehrenreich
A. Fortier
L. Fossati
S. Hoyer
L. Kiss
A. L. des Etangs
P. Maxted
I. Ribas
Y. Alibert
R. Alonso
G. A. Escudé
T. Bárczy
S.C.C. Barros
D. Barrado
W. Baumjohann
M. Beck
T. Beck
A. Bekkelien
X. Bonfils
W. Benz
L. Borsato
M.-D. Busch
J. Cabrera
S. Charnoz
A. Collier Cameron
C. Corral Van Damme
M. B. Davies
L. Delrez
M. Deleuil
O. Demangeon
B.O. Demory
Anders Erikson
Malcolm Fridlund
D. Futyan
A. Garciá Muñoz
Michaël Gillon
M. Guedel
P. Guterman
Kevin Heng
K. Isaak
G. Lacedelli
J. Laskar
M. Lendl
C. Lovis
A. Luntzer
D. Magrin
Valerio Nascimbeni
G. Olofsson
H. P. Osborn
R. Ottensamer
I. Pagano
Enric Palle
G. Peter
D. Piazza
Giampaolo P. Piotto
Don L. Pollacco
D. Queloz
Roberto Ragazzoni
N. Rando
H. Rauer
N. C. Santos
Gaetano Scandariato
D. Segransan
L. M. Serrano
D. Sicilia
A.E. Simon
Alexis M. S. Smith
S.G. Sousa
Manfred B. Steller
Nicolas Thomas
S. Udry
V. Van Grootel
N. A. Walton
T.G. Wilson
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 654 A159Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Other Physics Topics
Condensed Matter Physics
DOI
10.1051/0004-6361/202140345