The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
Articolo
Data di Pubblicazione:
2021
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.
Tipologia CRIS:
03A-Articolo su Rivista
Keywords:
Planetary systems
Elenco autori:
Gy. M. Szabò; D. Gandolfi; A. Brandeker; Sz. Csizmadia; Z. Garai; N. Billot; C. Broeg; D. Ehrenreich; A. Fortier; L. Fossati; S. Hoyer; L. Kiss; A. Lecavelier des Etangs; P. F. L. Maxted; I. Ribas; Y. Alibert; R. Alonso; G. Anglada Escud??; T. B??rczy; 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. D. S. Demangeon; B.-O. Demory; A. Erikson; M. Fridlund; D. Futyan; A. Garc??a Mu??oz; M. Gillon; M. Guedel; P. Guterman; K. Heng; K. G. Isaak; G. Lacedelli; J. Laskar; M. Lendl; C. Lovis; A. Luntzer; D. Magrin; V. Nascimbeni; G. Olofsson; H. P. Osborn; R. Ottensamer; I. Pagano; E. Pall??; G. Peter; D. Piazza; G. Piotto; D. Pollacco; D. Queloz; R. Ragazzoni; N. Rando; H. Rauer; N. C. Santos; G. Scandariato; D. S??gransan; L. M. Serrano; D. Sicilia; A. E. Simon; A. M. S. Smith; S. G. Sousa; M. Steller; N. Thomas; S. Udry; V. Van Grootel; N. A. Walton; T. G. Wilson
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