Upper panel: normalized spectra of the Hα line of 1  Del obtained at different places of a stellar image. Spectra were observed one after another during one night. They were obtained by positioning the slit to the left (L), central (C), and right (R) part of the stellar image. In this plot, spectra of (L) and (R) are shifted down by 0.5 and 1.0, respectively. Lower panel: differences between the central (C) spectrum and the left (L) and right (R) spectra. The difference (C−R) is shifted down by 0.5. Velocities in both panels are expressed with respect to the centre of the Hα line.