Szabo, GM, Gandolfi, D, Brandeker, A, Csizmadia, S, Garai, Z, Billot, N, Broeg, C, Ehrenreich, D, Fortier, A, Fossati, L, Hoyer, S, Kiss, L, des Etangs, AL, 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, M-D, Cabrera, J, Charnoz, S, Cameron, AC, Van Damme, CC, Davies, MB, Delrez, L, Deleuil, M, Demangeon, ODS, Demory, B-O, Erikson, A, Fridlund, M, Futyan, D, Munoz, AG, 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 and 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 and Astrophysics, 654. ISSN 0004-6361

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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.

Item Type: Article
Additional Information: The final version of this article and all relevant information related to it, including copyrights, can be found on the publisher website at;
Subjects: Q Science > Q Science (General)
Q Science > QA Mathematics
Q Science > QB Astronomy
Q Science > QB Astronomy > QB460 Astrophysics
Q Science > QB Astronomy > QB600 Planets. Planetology
Q Science > QC Physics
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Related URLs:
Depositing User: Symplectic
Date Deposited: 22 Dec 2021 09:13
Last Modified: 11 Feb 2022 11:05

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