Abstract

A revised MK classification for stars in the S-SC-C sequence is presented which provides convenient abundance classes that are primarily a measure of the C/O ratio. The stars are classified in terms of temperature type and abundance index, and intensities of ZrO and TiO are also taken into account. The assignment of temperature types and abundance classes is discussed, classification criteria are described, and the scale of temperature types is shown to be consistent in principle. The spectral sequence in the blue at approximately the temperature of an M4 giant is illustrated, along with the temperature sequence in the red region of SC stars.