Atlas of Stellar Spectra

Abstract: 

"The Atlas of Stellar Spectra and the accompanying outline have been prepared from the viewpoint of the practical stellar astronomer. Problems connected with the astrophysical interpretation of the spectral sequence are not touched on; as a consequence, emphasis is placed on ``ordinary'' stars. These are the stars most important statistically and the only ones suitable for large-scale investigations of galactic structure. The plan of the Atlas can be stated as follows: a) To set up a classification system as precise as possible which can be extended to stars of the eighth to twelfth magnitude with good systematic accuracy. The system should be as closely correlated with color temperature (or color equivalent) as is possible. The criteria used for classification should be those which change most smoothly with color equivalent. b) Such a system as described under (a) requires a classification according to stellar luminosity, that is, the system should be two-dimensional. We thus introduce a vertical spectral type, or luminosity class; then, for a normal star, the spectrum is uniquely located when a spectral type and a luminosity class are determined. The actual process of classification is carried out in the following manner: (1) an approximate spectral type is determined; (2) the luminosity class is determined; (3) by comparison with stars of similar luminosity an accurate spectral type is found."

English Abstract: 

"The Atlas of Stellar Spectra and the accompanying outline have been prepared from the viewpoint of the practical stellar astronomer. Problems connected with the astrophysical interpretation of the spectral sequence are not touched on; as a consequence, emphasis is placed on ``ordinary'' stars. These are the stars most important statistically and the only ones suitable for large-scale investigations of galactic structure. The plan of the Atlas can be stated as follows: a) To set up a classification system as precise as possible which can be extended to stars of the eighth to twelfth magnitude with good systematic accuracy. The system should be as closely correlated with color temperature (or color equivalent) as is possible. The criteria used for classification should be those which change most smoothly with color equivalent. b) Such a system as described under (a) requires a classification according to stellar luminosity, that is, the system should be two-dimensional. We thus introduce a vertical spectral type, or luminosity class; then, for a normal star, the spectrum is uniquely located when a spectral type and a luminosity class are determined. The actual process of classification is carried out in the following manner: (1) an approximate spectral type is determined; (2) the luminosity class is determined; (3) by comparison with stars of similar luminosity an accurate spectral type is found."

Alternative Title: 
MK Spectral Classification System
English Title: 
Atlas of Stellar Spectra
Author: 
W. W. Morgan
Philip C. Keenan
Edith Kellman
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Address: 
Ohio State University, Columbus, OH, United States