The Period-Luminosity and the Period-Spectrum Relations of Cluster-Type Cepheids.

The results of the present discussion are based on the material of M. Schwarzschild for 43 cluster-type variables of types a and b in the globular cluster M 3. It is pointed out that the color-magnitude diagram of these variables shows a descending branch resembling that of the main sequence. It is shown that this characteristic, combined with the theoretical period-density relation (satisfied by these variables), gives, as a consequence, the period-spectrum and the period-luminosity relations