Wiggle correction in epoch 1 of HD 209458b, for exposures at index 60 (top panel) and 88 (bottom panel). Blue and red profiles show spectra before and after correction, respectively. Flux spectra are normalized by the stellar continuum (estimated from the corrected data; Sect. 7.1) and offset for clarity. The dashed black line represents the normalized continuum unity. Transmission spectra, shown at the top of the panels and calculated with the master out-of-transit spectrum, highlight wiggle patterns strong enough to be visible in the flux spectra.