Luminosity effects at spectral type M2 in the region around the calcium infrared triplet. The solid line corresponds to the M2Ib standard HD 10465, and the dashed line to the M2III standard HD 219734 (Garcia 1989). Both spectra have been ratioed to their best-fitting 7th-degree polynomial (fit to the whole 6000 <  λ(Å) < 9000 range) to facilitate comparison. The spectral lines used in this work as luminosity class discriminants are indicated.