Published online by Cambridge University Press: 25 April 2016
A study has been made of the upper main-sequence stars in several young clusters, in an attempt to determine a well-defined effective temperature scale for the B stars, and to compare the observed atmospheric parameters with the recent theoretical evolutionary tracks in the H-R diagram (Iben, 1965, Hofmeister et al, 1964, Kippenhahn et al., 1965). Each of the clusters studied contains at least one peculiar A star of the Si λ-4200 type, and this afforded an excellent opportunity for a study of the evolution of these stars.