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Arxiv: Transiting exoplanets with the Mid-InfraRed Instrument on board the James Webb Space Telescope: From simulations to observations Published: 3/1/2024 7:09:23 PM Updated: 3/1/2024 7:09:23 PM

Paper abstract: The James Webb Space Telescope (JWST) has now started its exploration ofexoplanetary worlds. In particular, the Mid-InfraRed Instrument (MIRI) with itsLow-Resolution Spectrometer (LRS) carries out transit, eclipse, and phase-curvespectroscopy of exoplanetary atmospheres with unprecedented precision in a sofar almost uncharted wavelength range. The precision and significance in thedetection of molecules in exoplanetary atmospheres rely on a thoroughunderstanding of the instrument itself and accurate data reduction methods.This paper aims to provide a clear description of the instrumental systematicsthat affect observations of transiting exoplanets through the use ofsimulations. We carried out realistic simulations of transiting-exoplanetobservations with the MIRI LRS instrument that included the model of theexoplanet system, the optical path of the telescope, the MIRI detectorperformances, and instrumental systematics and drifts that could alter theatmospheric features we are meant to detect in the data. After introducing ourpipeline, we show its performance on the transit of L168-9b, asuper-Earth-sized exoplanet observed during the commissioning of the MIRIinstrument. This paper provides a better understanding of the data themselvesand of the best practices in terms of reduction and analysis throughcomparisons between simulations and real data. We show that simulationsvalidate the current data-analysis methods. Simulations also highlightinstrumental effects that impact the accuracy of our current spectralextraction techniques. These simulations are proven to be essential in thepreparation of JWST observation programs and help us assess the detectabilityof various atmospheric and surface scenarios.