Results from PCA. Top: solid black line is the mean PCA spectrum computing using all observed spectra obtained out to +70 d and covering the wavelength region 3950–7350 Å. Blue and red shaded regions correspond to the full range of Amplitude_i with blue (red) corresponding to negative (positive) values. Vertical gray regions correspond to He I (PC₂ panel) and H I (PC₃ panel) related features (same as in Fig. 2), indicating that variation in PC₂ corresponds strongly to Helium and in PC₃ to Hydrogen. Bottom: amplitude₂ versus Amplitude₃, color-coded by spectral subtype with the intensity of colors corresponding to the phase of the observed spectra following the multicolumn colorbar located to the right.