Top panel: example of raw spectrum (blue) for star 05244301-6943412 and the corresponding master-sky (black) we used to obtain the sky-subtracted spectrum (red). In the red spectrum sky emission lines have been correctly removed. A cosmic ray remains at ~ 6290 Å. Bottom panel: the sky-subtracted spectrum of 05244301-6943412 before (red) and after (blue) the correction for the telluric lines. The spectrum of the fast rotator is plotted in black to show the position of telluric features. The green spectrum is the co-added spectrum: the σ-clipping has removed the remaining cosmic rays and the signal-to-noise ratio is clearly improved compared to the single exposure. All spectra are plotted in the same scale, except for the fast rotator spectrum (it has been scaled for legibility).