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Target RA (J2000): 311.289703 and deg Target Dec (J2000): -31.34090 and deg Gaia GMag: 7.84 Programme ID: CH_PR130057 Programme Manager: SZABO PI of observing programme: Benz Title of programme: Pinning down a young planetary system: CHEOPS observations of AU Mic (CHAUMic) Abstract: We propose to carry out an intensive in-transit and out-of-transit CHEOPS observing campaign of the golden target AU Mic aiming at: • constraining the TTV signals of AU Mic b and c and measuring their masses. High-precision radial velocity observations of AU Mic are hampered by the activity of the star as recently shown by Zicher et al. 2022 (MNRAS 512 3060) who measured the masses of planet b and c with a precision of “only” 43 % and 30 % using more than 100 HARPS measurements evenly spread across one year. Conversely CHEOPS have proven to be very effective in measuring planet masses of near-resonant transiting systems such as TOI-1130 b and c for which a precision of ?9 % has been achieved exploiting the TTV method. Our program requires transit observations of planet b and c to be carried out in July August. • studying the evolution time-scale of active regions across the transit cord using AU Mic b as a “scanner”. Unbiased measurements of Rp/R? can be determined only by modeling the transit light curves along with the map of the occulted (and unocculted see below) spots. This requires CHEOPS multiple observations of the transits of AU Mic b at the 4 possible star-planet configurations. By observing spot-crossing events of transits occurring at the same stellar longitudes as in 2020 and 2021’s CHEOPS observations we will also assess whether the distribution of spots has evolved or not. On the other hand transit observations at stellar longitudes that have not yet b [truncated! Please see actual data for full text]