Cepheid variables and the Magellanic Clouds.

The Magellanic Cloud variables differ from variables in the Galaxy by the number of variables at different periods, by the period-amplitude relation, and by the mean color. Schematic evolutionary tracks are used to demonstrate how a proposed difference between Galactic evolution and Small Magellanic Cloud evolution might be responsible for the observed mean colors and frequencies of occurrence of cepheid variables with different periods. The frequency of short-period cep heids is seen to be a very sensitive indicator of some, not yet fully understood, aspect of abundances. It is demonstrated that the characteristic second-bump feature appearing in the light curves of cepheids with the period range from 7 to 15 days can be used to determine stellar mass and radius on the basis of calculations of interior motions.-