Classical Cepheid Pulsation Models. I. Physical Structure

The pulsation properties and modal stability of Cepheid models are investigated in both linear and nonlinear regimes. The linear survey is based on nonadiabatic, radiative models, whereas the nonlinear one relies on full-amplitude models that include a nonlocal and time-dependent treatment of stellar convection. To account for Cepheid pulsation characteristics over a substantial portion of the region in which they are expected to be pulsationally unstable, a wide range of stellar masses (5≤M/M≤11) and effective temperatures (4000≤Te≤7000 K) was adopted. The luminosity of each model was fixed according to the mass-luminosity (ML) relations predicted by evolutionary models that either neglect or take into account a mild convective core overshooting. Moreover, in order to estimate the effects of the helium and metal content on the limiting amplitude behavior of both Magellanic Clouds and Galactic Cepheids we adopted three different chemical compositions, namely, Y=0.25, Z=0.004; Y=0.25, Z=0.008; and Y=0.28, Z=0.02. For each set of input parameters we investigated the modal stability of both fundamental and first-overtone modes.