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Target RA (J2000): 151.659790 and deg Target Dec (J2000): 18.63406 and deg Gaia GMag: 9.94 Programme ID: CH_PR230023 PI of observing programme: Fairnington Title of programme: The TTVs of a compact planetary system around an early-type star with CHEOPS Abstract: The planetary formation and evolution process around early type stars are poorly mapped. We propose to use CHEOPS to observe a benchmark multi-planetary system (TOI-5126) around a young F star. The system hosts a Neptune sized planet with a 5.46 day orbital period (TOI-5126.01) and a sub-Neptune on a 17.9 day orbit (TOI-5126.02). Further there are potential Transit Timing Variations (TTVs) exhibited in the TESS data at the 5-minute level. We will use CHEOPS to validate the candidate TTV signals of TOI-5126.01 as well as put mass constraints on the planet. These observations are essential for the confirmation of the planetary nature of the TOI-5126 system enabling future atmospheric characterization and density measurements. [truncated! Please see actual data for full text]