A hydrodynamical survey of the pulsational properties of first overtone Galactic Cepheids is presented. The goal of this study is to reproduce their observed light-and radial velocity curves. The comparison between the models and the observations is made in a quantitative manner on the level of the Fourier coefficients. Purely radiative models fail to reproduce the observed features, but convective models give good agreement. It is found that the sharp features in the Fourier coefficients are indeed caused by the P 1 /P 4 = 2 resonance, despite the very large damping of the 4th overtone. For the adopted mass-luminosity relation the resonance center lies near a period of 4. d 2 ± 0.2 as indicated by the observed radial velocity data, rather than near 3. d 2 as the light-curves suggest.

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Abstract. The physical and numerical ingredients of the Vienna nonlinear model for radially pulsating stars are presented. Stellar pulsations are investigated by solving the full system of radiation hydrodynamics including a time-dependent formulation of turbulent convection. The numerical solution method comprises a state-of-the-art adaptive grid algorithm which provides a powerful tool for resolving and tracking the most important ionization zones. Several already published applications to pulsating stars in the classical instability strip demonstrate that the model is able to reproduce important observational properties like RR Lyrae light curves or double mode pulsations.

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The luminosities, e †ective temperatures, and metallicities that are derived empirically by & Kova cs Jurcsik from the light curves of a large number of globular cluster and Ðeld RRab and RRc stars are compared to theoretical RR Lyrae models. The strong luminosity dependence of the empirical blue and red edges (log L vs.diagram) is in disagreement with that of both radiative and convective log T eff models. A reexamination of the theoretical uncertainties in the modeling leads us to conclude that the disagreement appears irreconcilable.