Reduced 2D science frame of S4 as assessed from the pipeline. We show a single nodding position. The color indicates flux, where red and blue are high and low flux, respectively. The spatial position is with respect to the center of the slit. The figure is centered around the [S II] 671.6,673.1 nm lines (the two bright lines on the right) and the He I 667.8 nm line (the bright line on the left), all originating from the nebula. The three weak lines on the right are nebular Fe I lines. The continuum of S4 is visible in the lower part of the 2D frame. Additionally, some nebular continuum is visible. At the top, some weak continuum from an object not analyzed in this work.