Spectroscopic Time Series Performance of the Mid-infrared Instrument on the JWST

Abstract We present here the first ever mid-infrared spectroscopic time series observation of transiting exoplanet L 168-9 b with Mid-Infrared Instrument (MIRI) on James Webb Space Telescope. The data were obtained as part MIRI commissioning activities, to characterize performance Low Resolution Spectroscopy (LRS) mode for these challenging observations. To assess LRS performance, we performed two independent analyses data. find that a single transit reached spectro-photometric precision ?50 ppm in 7–8 ? m range at R = 50, consistent ?25 systematic noise. derived band averaged depth is 524 ± 15 and 547 13 applied analysis methods, respectively, recovering known within 1 ? . measured noise planet’s transmission spectrum approximately 15%–20% higher than random simulations over wavelengths 6.8 ? ? 11 m. observed an larger excess shortest up factor two, which possible causes are discussed. This was achieved limited in-flight calibration data, demonstrating future potential characterization atmospheres.