A determination of the characteristics of Cepheids from B-type companions

Photometry (uvbyβ) of five cepheids with B-type companions has been utilized to derive the spectral types and apparent magnitudes of the companions. By utilizing the period-luminosity relation it is possible to estimate the absolute magnitudes of the companions since the differences in magnitude between the companions and cepheids are known. The spectral types and absolute magnitudes of the B-type components indicate they are all evolved from the zero-age main sequence. By utilizing the ages of the B stars we can derive the ages of the cepheids under the assumptions that both stars of a binary were formed at the same time and the cepheids are more evolved than their B components. A period-age relation of the form log tsub(age) = 8.60 - 0.83 log P is found. Minimum masses of the cepheids can also be estimated from the data. No evidence of large mass loss is evident in the intermediate-band photometry of cepheids. (Auth.)