On the atmospheric abundances of seven Am SB2 systems.

The observed characteristics of the metallic-line A type stars are described and the theories to account for their apparent abundance anomalies are reviewed. The mounting of an observing programme for the determination of the compositions of the component stars of a number of double-lined (SB2) systems and the reduction of the spectroscopic and spectrophotometric data are discussed. An account is given of a method for the determination of the atmospheric parameters and the component star luminosity ratios in SB2 systems and also of the abundance analysis procedure through the differential curve of growth. The results suggest an evolutionary origin for the metallic-line A stars and a scheme, based on the element separation mechanism, is put forward.