I-band model spectrum of supergiant stars obtained by fitting at each wavelength the flux-normalized (at 0.88 μm) sample spectra along SpTs. The model spectrum for different SpTs is offset for displaying purposes and the SpT is given. The green and red regions mark the bandpasses of the newly defined indices and their adjacent continuum, respectively (see Table 1). In particular the light green, green and dark green regions mark the Pa, Ca, Mg and FeClTe features, respectively. Some relevant absorption features are marked.