The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
Journal
Date Issued
2021
Author(s)
Szabó, Gy. M.
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Gandolfi, D.
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Brandeker, A.
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Csizmadia, Sz.
•
Garai, Z.
•
Billot, N.
•
Broeg, C.
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Ehrenreich, D.
•
Fortier, A.
•
Fossati, L.
•
Hoyer, S.
•
Kiss, L.
•
Lecavelier des Etangs, A.
•
Maxted, P. F. L.
•
Ribas, I.
•
Alibert, Y.
•
Alonso, R.
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Anglada Escudé, G.
•
Bárczy, T.
•
Barros, S. C. C.
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Barrado, D.
•
Baumjohann, W.
•
Beck, M.
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Beck, T.
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Bekkelien, A.
•
Bonfils, X.
•
Benz, W.
•
•
Busch, M. -D.
•
Cabrera, J.
•
Charnoz, S.
•
Collier Cameron, A.
•
Van Damme, C. Corral
•
Davies, M. B.
•
Delrez, L.
•
Deleuil, M.
•
Demangeon, O. D. S.
•
Demory, B. -O.
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Erikson, A.
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Fridlund, M.
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Futyan, D.
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García Muñoz, A.
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Gillon, M.
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Guedel, M.
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Guterman, P.
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Heng, K.
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Isaak, K. G.
•
Lacedelli, G.
•
Laskar, J.
•
Lendl, M.
•
Lovis, C.
•
Luntzer, A.
•
•
•
Olofsson, G.
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Osborn, H. P.
•
Ottensamer, R.
•
•
Pallé, E.
•
Peter, G.
•
Piazza, D.
•
Piotto, G.
•
Pollacco, D.
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Queloz, D.
•
•
Rando, N.
•
Rauer, H.
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Santos, N. C.
•
•
Ségransan, D.
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Serrano, L. M.
•
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Simon, A. E.
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Smith, A. M. S.
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Sousa, S. G.
•
Steller, M.
•
Thomas, N.
•
Udry, S.
•
Van Grootel, V.
•
Walton, N. A.
•
Wilson, T. G.
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 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....
Volume
654
Start page
A159
Issn Identifier
0004-6361
Rights
open.access
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