Spectral Classifications and Multi-Band Colour Indices

Abstract

During the past three years there has been much activity in the field of spectral classification by photographic and photoelectric techniques. The general tendency of the spectral classification has been one of refinement of the criteria applied in visual classification, the more frequent appearance of criteria based on equivalent widths measured in higher-dispersion spectra and the use of narrow-band photometry on individual often rather weak spectral lines. In the area of objective prism classification important extensive programmes are under way at many observatories. Here, the increased interest in and importance of automation of data available on spectral plates is perhaps most obvious.