Photoelectric two-dimensional spectral classification of M supergiants

A photoelectric system defined by eight narrow bands between 0.7 and 1.1 microns has been used to measure nearly all M supergiants that have been classified on the MK system. The photometric TiO and CN indices reproduce the two-dimensional MK classifications to the accuracy of the MK types themselves. Mean fluxes and spectral classifications are presented for 128 stars.