Mean out-of-transit spectrum of the KELT-9 system as observed by HARPS-N, produced by stitching together the individual spectral orders after correction of the blaze function. The blue and black lines show the spectrum before and after telluric correction. The smaller panel shows the telluric water band that is highlighted in grey in detail, demonstrating the effect of the telluric correction. The outlying points are residuals of deep telluric absorption and a small number of emission lines that have remained uncorrected.