Effects of telluric removal on the signal from KELT-9 b. Left: best-fit Fe I emission model Doppler-shifted based on the orbital parameters of KELT-9 b (panel a), injected on top of the first night of HARPS-N data, and passed through the analysis described in Sect. 2.2.2. The signal is recovered with evident alterations, as shown in the reference frame of the observer (panel b) and in the planet’s rest frame (panel c). Top-right: recovered amplitude of a strong injected Fe line as a function of orbital phase (solid) versus its amplitude at injection (dashed). Bottom-right: percent loss of the Fe signal due to the telluric-removal analysis. Nearly 100% of the signal is lost around quadrature.