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The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and Transit Timing Variations as seen by CHEOPS and TESS

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arxiv 2108.02149 v1 pith:ZUY5GSRS submitted 2021-08-04 astro-ph.EP astro-ph.SR

Gy.M. Szabó , D. Gandolfi , A. Brandeker , Sz. Csizmadia , Z. Garai , N. Billot , C. Broeg , D. Ehrenreich
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A. Fortier L. Fossati S. Hoyer L. Kiss A. Lecavelier des Etangs P.F.L. Maxted I. Ribas Y. Alibert R. Alonso G. Anglada 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.D.S. Demangeon B.-O. Demory A. Erikson M. Fridlund D. Futyan A. García Muñoz M. Gillon M. Guedel P. Guterman K. Heng K.G. Isaak G. Lacedelli J. Laskar M. Lend C. Lovis A. Luntzer D. Magrin V. Nascimbeni G. Olofsson H.P. Osborn R. Ottensamer I. Pagano E. Pallé G. Peter D. Piazza G. Piotto D. Pollacco D. Queloz R. Ragazzoni N. Rando H. Rauer N.C. Santos G. Scandariato D. Ségransan 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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classification astro-ph.EPastro-ph.SR
keywords stellartransitcheopsobservedaccuracycommensurabilityexoplanetfind
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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 (ASAS) from the ground. The refined orbital period of AU Mic b is 8.462995 \pm 0.000003 d, whereas the stellar rotational period is P_{rot}=4.8367 \pm 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 minutes. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 minutes. We find that the outer companion, AU Mic c may cause the observed TTVs.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Unstable magnetospheric accretion on the T Tauri star TW Hya

    astro-ph.SR 2026-07 accept novelty 4.5 of 10

    TW Hya’s large-scale field is a ~0.83 kG tilted dipole that varies yearly; accretion is unstable (rmag/rcor ≈ 0.33–0.40) and no close-in planet is detected above ~0.3–1 Mjup.

  2. CHEOPS photometry from 2024 reveals a reversal in the transit-timing variations of AU Mic c

    astro-ph.EP 2026-08 conditional novelty 4.0 of 10

    2024 CHEOPS transit timings of AU Mic c show a reversal of the 2023 timing offset, indicating the large deviation was not sustained.

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