Letter to the Editor

Transit timing variations of AU Microscopii b and c^⋆

¹ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szent Imre h. u. 112, 9700 Szombathely, Hungary
e-mail: szgy@gothard.hu
² MTA-ELTE Exoplanet Research Group, Szent Imre h. u. 112, 9700 Szombathely, Hungary
³ Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
⁴ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
⁵ Dipartimento di Fisica, Universita degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino, Italy
⁶ Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
⁷ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, Versoix, Switzerland
⁸ Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
⁹ Center for Space and Habitability, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
¹⁰ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
¹¹ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹² Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98 Bis Blvd. Arago, 75014 Paris, France
¹³ Aix Marseille Univ., CNRS, CNES, LAM, 38 Rue Frédéric Joliot-Curie, 13388 Marseille, France
¹⁴ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
¹⁵ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
¹⁶ Departamento de Astrofisica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁷ Institut de Ciencies de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
¹⁸ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹⁹ ADMATIS, 5. Kandó Kálmán Street, 3534 Miskolc, Hungary
²⁰ Depto. de Astrofisica, Centro de Astrobiologia (CSIC-INTA), ESAC Campus, 28692 Villanueva de la Cañada, Madrid, Spain
²¹ Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
²² Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
²³ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
²⁴ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
²⁵ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
²⁶ Université de Paris, Institut de Physique du Globe de Paris, CNRS, 75005 Paris, France
²⁷ Centre for Mathematical Sciences, Lund University, Box 118 221 00 Lund, Sweden
²⁸ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
²⁹ Leiden Observatory, University of Leiden, PO Box 9513 2300 RA Leiden, The Netherlands
³⁰ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
³¹ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
³² Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³³ Science and Operations Department – Science Division (SCI-SC), Directorate of Science, European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³⁴ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
³⁵ IMCCE, UMR 8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 Av. Denfert-Rochereau, 75014 Paris, France
³⁶ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
³⁷ Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna, Austria
³⁸ INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
³⁹ Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
⁴⁰ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universita degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴¹ ESTEC, European Space Agency, 2201 AZ Noordwijk, The Netherlands
⁴² Center for Astronomy and Astrophysics, Technical University Berlin, Hardenberstrasse 36, 10623 Berlin, Germany
⁴³ Institut für Geologische Wissenschaften, Freie Universität Berlin, 12249 Berlin, Germany
⁴⁴ Space Science Data Center, ASI, Via del Politecnico snc, 00133 Roma, Italy
⁴⁵ INAF, Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, RM, Italy
⁴⁶ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴⁷ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter Sétány 1/A, 1117 Budapest, Hungary

Received: 10 January 2022
Accepted: 1 February 2022

Abstract

Here we report large-amplitude transit timing variations (TTVs) for AU Microcopii b and c as detected in combined TESS (2018, 2020) and CHEOPS (2020, 2021) transit observations. AU Mic is a young planetary system with a debris disk and two transiting warm Neptunes. A TTV on the order of several minutes was previously reported for AU Mic b, which was suggested to be an outcome of mutual perturbations between the planets in the system. In 2021, we observed AU Mic b (five transits) and c (three transits) with the CHEOPS space telescope to follow-up the TTV of AU Mic b and possibly detect a TTV for AU Mic c. When analyzing TESS and CHEOPS 2020−2021 measurements together, we find that a prominent TTV emerges with a full span of ≥23 min between the two TTV extrema. Assuming that the period change results from a periodic process –such as mutual perturbations– we demonstrate that the times of transits in the summer of 2022 are expected to be 30−85 min later than predicted by the available linear ephemeris.