Spectral types and their uses
Philip C. Keenan · Publications of the Astronomical Society of the Pacific · 1987
The principles involved in setting up any viable system of spectral classification are discussed. Their application is illustrated by reviewing the essential features of the original MK system of two dimensions and its extension to additional dimensions, particular attention being paid to the Revised MK System as applied to stars of types G0 through M8. The domain of wavelengths within which stars at a given temperature can be classified on a consistent system is defined. The application of spectral types to the preparation of observing programs, to statistical studies of the distribution of selected groups of stars, and to the direct estimation of physical properties of stars is discussed briefly.