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Target RA (J2000): 351.770172119141 and deg Target Dec (J2000): -1.28627002239227 and deg Gaia GMag: 9.841 Programme ID: CH_PR159006 Programme Manager: ZULETA PI of observing programme: Benz Title of programme: SoM - TRACE Abstract: The TRACE (Measuring the TRansit light sourCe Effect with CHEOPS) program aims to use the CHEOPS telescope to characterize the transit light source effect (TLSE) for exoplanet targets scheduled for observation with the JWST. This effort addresses a critical challenge in exoplanet atmosphere analysis: contamination from stellar activity such as star spots and faculae which can skew measurements of planetary atmospheres by introducing variability in observed spectra. The program will conduct high-precision photometric observations in the optical band an essential range that JWST does not cover but is critical to identify and mitigate stellar contamination in transmission spectra. Focusing on two primary targets in a first stage --TOI-1416 and GJ9827--the project plans long-baseline in and out-of-transit observations spread across a few stellar rotations to model activity-related flux variations. These findings are expected to help the JWST data interpretation of the planets atmosphere and support the broader scientific community by making data publicly available immediately. By characterizing activity in CHEOPS-observed systems TRACE aims to enhance our understanding of exoplanet atmospheres and prepare for future synergy with upcoming missions such as PANDORA. [truncated! Please see actual data for full text]