Effects of Stellar Rotation on Spectral Classification

Abstract Stellar rotation may affect the strengths of lines used in spectral classification because of effects of plate resolution and also because of physical changes in the rotating stellar atmospheres. In the first case, the importance of using standard stars with appropriate rotational line broadening in classifying spectra of relatively high dispersion (resolution) is emphasized. Rotational effects on weak lines in general and on the Balmer lines may cause systematic errors in the assignment of spectral types and luminosity classes unless the standard stars are chosen with line broadening similar to that of the star to be classified. With regard to physical changes in the rotating atmospheres, we have extended the earlier work of Collins to include the Balmer lines plus additional lines of He I and Si II which are important in spectral classification over a wider range of spectral types.