[en] The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter-McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with VLT/ESPRESSO, CHEOPS, and NGTS. After correcting for flares and for the magnetic activity of the host star, and accounting for transit-timing variations, we find the sky-projected spin-orbit angle of planet c to be in the range $\lambda _c=67.8_{-49.0}^{+31.7}$ degrees (1-σ). We examine the possibility that planet c is misaligned with respect to the orbit of the inner planet b ($\lambda _b=-2.96_{-10.30}^{+10.44}$), and the equatorial plane of the host star, and discuss scenarios that could explain both this and the planet’s high density, including secular interactions with other bodies in the system or a giant impact. We note that a significantly misaligned orbit for planet c is in some degree of tension with the dynamical stability of the system, and with the fact that we see both planets in transit, though these arguments alone do not preclude such an orbit. Further observations would be highly desirable to constrain the spin-orbit angle of planet c more precisely.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Yu, H ; Sub-department of Astrophysics, Department of Physics , University of Oxford, Oxford OX1 3RH,
Garai, Z ; HUN-REN–ELTE Exoplanet Research Group , Szent Imre h. u. 112, H-9700 Szombathely, ; ELTE Gothard Astrophysical Observatory , Szent Imre h. u. 112, H-9700 Szombathely, ; Astronomical Institute, Slovak Academy of Sciences , 05960 Tatranská Lomnica,
Cretignier, M ; Sub-department of Astrophysics, Department of Physics , University of Oxford, Oxford OX1 3RH,
Szabó, Gy M; HUN-REN–ELTE Exoplanet Research Group , Szent Imre h. u. 112, H-9700 Szombathely, ; ELTE Gothard Astrophysical Observatory , Szent Imre h. u. 112, H-9700 Szombathely,
Aigrain, S; Sub-department of Astrophysics, Department of Physics , University of Oxford, Oxford OX1 3RH,
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Correia, A C M ; CFisUC, Departamento de Física, Universidade de Coimbra , 3004-516 Coimbra,
Klein, B ; Sub-department of Astrophysics, Department of Physics , University of Oxford, Oxford OX1 3RH,
Brandeker, A; Department of Astronomy, Stockholm University, AlbaNova University Center , 10691 Stockholm,
Owen, J E; Astrophysics Group, Department of Physics , Imperial College London, Prince Consort Road, London SW7 2AZ, ; Department of Earth, Planetary, and Space Sciences, University of California , Los Angeles, CA 90095,
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Winn, J N; Department of Astrophysical Sciences, Princeton University , Princeton, NJ 08544,
Heitzmann, A; Observatoire astronomique de l’Université de Genéve , Chemin Pegasi 51, 1290 Versoix,
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Wilson, T G; Department of Physics, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL, United Kingdom ; Centre for Exoplanets and Habitability, University of Warwick , Coventry CV4 7AL,
Gill, S; Department of Physics, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL, United Kingdom
Kriskovics, L; Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences , Konkoly Thege út 15-17., H-1121, Budapest,
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Doyle, L; Department of Physics, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL, United Kingdom ; Centre for Exoplanets and Habitability, University of Warwick , Coventry CV4 7AL,
Edwards, B; SRON Netherlands Institute for Space Research , Niels Bohrweg 4, 2333 CA Leiden,
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Kiss, L L; Konkoly Observatory, Research Centre for Astronomy and Earth Sciences , 1121 Budapest, Konkoly Thege Miklós út 15-17, ; ELTE Eötvös Loránd University, Institute of Physics , Pázmány Péter sétány 1/A, 1117 Budapest,
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