Observed spectra around the Hα line (left column), for Night 1 (first row), Night 2 (second row), Night 3 (third row) and Night 4 (fourth row). The three first nights were observed with HARPS-N and the last night, with CARMENES. The spectra are normalised to the same continuum level (see colour bar) and moved to the stellar rest frame. In the y-axis we show the spectrum number starting from zero and in the x-axis the velocity in km s⁻¹. The narrow lines correspond to telluric contamination and the deepest central line (at 0 km s ⁻¹) corresponds to the centre of the Hα line core. Second and third columns: S/N and the airmass variation during the night, respectively. The S/N per pixel is extracted in the continuum near the Hα line, specifically around 6600 Å as the Hα line for this target is very broad due to its rapid rotation. The red S/N values correspond to the spectra which are not considered in our analysis. In particular, we observe a stable S/N during Night 1. Night 2 shows a drop in the S/N for the presence of a cloud around spectrum number 25 and two stops of the instrument around spectrum number 50 and 100 because GIANO-B suddenly aborted itself and it was necessary to restart the exposure with both the HARPS-N and GIANO-B instruments.