Non-linear radiative models of post-AGB stars:: Application to HD 56126

In order to study in a general manner the pulsations of the post-AGB stars we performed a grid of non-linear radiative low-mass, high-luminosity models in a wide range of T-eff, L and M. Theoretical bolometric light curves and radial velocity curves were computed as well as their associated power spectra. We have also examined the behaviour of these models according to the stellar mass, the chemical composition and the opacity tables we have used in the code. Concerning the carbon rich post-AGB star HD 56126, the models best found to fit its observational characteristics are X = 0.7, Z = 0.004, M = 0.8M., L = 6000-7000 L. and T-eff less than or equal to 5850 K. Models computed with smaller mass fail to reproduce both the period and the pulsational amplitude of HD 56126, which is quite different from the pulsational amplitude of the RV Tauri stars. The previously analysed spectroscopic and photometric variations of HD 56126 appear to be consistent with a non-regular radial pulsation where the dominant pulsation mode is the first overtone. In the course of the pulsation, moderate shock waves are repeatedly generated and they propagate throughout the stellar atmosphere. They provoke a complex, asynchronous motion of the outer layers.