On the theoretical period-radius relation of classical Cepheids

We present the results of a comprehensive theoretical investigation of the period-radius relation of classical Cepheids based on new sequences of full-amplitude, nonlinear, convective models constructed by adopting a wide range of both stellar masses and chemical compositions. In the period range 0.9 less than or equal to log P less than or equal to 1.8, very good agreement is found between theoretical predictions and current available data, whereas outside this range, at both shorter and longer periods, nonlinear radii attain intermediate values between empirical relations based on different Baade-Wesselink methods and photometric bandpasses.