Influence of telluric contamination by H₂O and O₂ molecules on a spectrum of KELT-11 from HARPS observations (red CCD). We note that the resulting total correction is shown, as individual spectrum correction varies greatly case-by-case. Top: applied telluric correction obtained using Molecfit. Bottom: zoomed-in telluric correction around Na doublet (~5890 Å), black being the corrected spectrum and red the noncorrected one.