Examples of noise injections around the H_α = 6562.79 Åline on the spectra time series of HD 128621 (YARARA uncorrected)for different S∕N_cont values. Fromtop to bottom: S∕N_cont = 592 (nominal median values of the observations), 250, 150, and 50. This example also illustrates the approximated required S∕N_cont to detect and correct for the systematics using YARARA. For instance, at S∕N_cont=50, the pattern of interference and the H_α chromospheric variation are not detected whereas some of the telluric lines in that wavelength range are still visible.