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Published online by Cambridge University Press: 07 August 2017
“Although the evidence presented in the preceding discussion is still very fragmentary, there can be no doubt that, in dealing with galaxies, we have to distinguish two types of stellar populations, one which is represented by the ordinary H-R diagram (type I), the other by the H-R diagram of the globular clusters (type II). Characteristic of the first type are highly luminous O- and B-type stars and open clusters, of the second, globular clusters and short-period Cepheids…it should be pointed out that these same two types of stars were recognized by Oort as early as 1926. Oort showed that the high-velocity stars of our galaxy (our type II) are of a kind quite different from the slowmoving stars (type I) which predominate in the solar neighborhood.”