On the frequency-period distribution of galactic cepheids

An analysis is made of the frequency-period distribution of galactic Cepheids. The observed distribution shows that the density of Cepheids, the period, P1, of the maximum and the width of the distribution vary with galactocentric distance. From a comparison with the theoretical distribution constraints on the stellar evolutionary models and on the width of the instability strip are derived. Assuming Serrano's (1978) IMF it is shown that: a) in the case of the Galaxy, Cepheids show no evidence for a two component birthrate with higher amplitudes for large masses, b) for Cepheids with period longer than P1, the lifetime as a Cepheid varies as P-sup(0.65), c) the star formation rate, SFR, in the solar neighborhood is 1.2 stars pc-2 Gyr-1,d) the local gradient of heavy elements abundance, Z, is nabla log Z = -0.12 kpc-1, e) the local gradient of SFR is nabla logSFR = -0.16 kpc-1. (author)