For each star and observing campaign, the mean spectra and relative variability distributions are plotted on the left side. The HeI5876, NaID, [OI]6300 and Hα regions are enlarged on the right side, for a better visualization. The mean spectrum is given by I_i,k, and the relative variability by σ_k/I_rel,k, being σ_k = [(I_i,k − I_rel,k)²]^1/2. The subindex k refers to each spectral bin and the subindex i to each one of the N spectra per observing campaign. The relative variability plots provide information on the strength and wavelength position of the changes in the line intensity (Johns & Basri 1995).