The changing face of AU Mic b : stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
Abstract
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 P-rot = 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.
Citation
Szabo , G M , Gandolfi , D , Brandeker , A , Csizmadia , S , Garai , Z , Billot , N , Broeg , C , Ehrenreich , D , Fortier , A , Fossati , L , Hoyer , S , Kiss , L , Lecavelier des Etangs , A , Maxted , PFL , Ribas , I , Alibert , Y , Alonso , R , Escude , GA , Barczy , T , Barros , SCC , Barrado , D , Baumjohann , W , Beck , M , Beck , T , Bekkelien , A , Bonfils , X , Benz , W , Borsato , L , Busch , MD , Cabrera , J , Charnoz , S , Cameron , AC , Van Damme , CC , Davies , MB , Delrez , L , Deleuil , M , Demangeon , ODS , Demory , BO , Erikson , A , Fridlund , M , Futyan , D , Muñoz , A G , Gillon , M , Guedel , M , Guterman , P , Heng , K , Isaak , KG , Lacedelli , G , Laskar , J , Lendl , M , Lovis , C , Luntzer , A , Magrin , D , Nascimbeni , V , Olofsson , G , Osborn , HP , Ottensamer , R , Pagano , I , Palle , E , Peter , G , Piazza , D , Piotto , G , Pollacco , D , Queloz , D , Ragazzoni , R , Rando , N , Rauer , H , Santos , NC , Scandariato , G , Segransan , D , Serrano , LM , Sicilia , D , Simon , AE , Smith , AMS , Sousa , SG , Steller , M , Thomas , N , Udry , S , Van Grootel , V , Walton , NA & Wilson , TG 2021 , ' The changing face of AU Mic b : stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS ' , Astronomy & Astrophysics , vol. 654 , A159 . https://doi.org/10.1051/0004-6361/202140345
Publication
Astronomy & Astrophysics
Status
Peer reviewed
ISSN
0004-6361Type
Journal article
Rights
Copyright © ESO 2021. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the final published version of the work, which was originally published at https://doi.org/10.1051/0004-6361/202140345. .
Description
A.C.C. and T.W. acknowledge support from STFC consolidated grant number ST/M001296/1.Collections
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