Variability of the output spectra in two SOFIN subexposures taken with the quarter-wave plate angles separated by 90° taken around HJD 2 455 398.530. The lower two spectra, (I + V)₀ and (I − V)₀, correspond to the first subexposure, while the upper spectra, (I − V)₉₀ and (I + V)₉₀, correspond to the second subexposure. The strong effect of pulsations on the line profile shapes and the line positions is clearly visible between the spectra of the first subexposure with a duration of 20 min and the spectra of the second subexposure with the same duration.