Atmospheric Dynamics of Post-AGB Stars: New Results on the Nature of the Pulsation of HD 56126

We present a complete analysis of spectroscopic and photometric observations of HD 56126, a variable carbon-rich post-AGB star. In order to improve the knowledge of its pulsation and of its fundamental parameters, we have computed a set of linear and non-linear pulsating models relevant to the post-AGB stars. From two different observational data sets, we find a main pulsating period P = 36.8 ± 0.2 days. The spectroscopic and photometric variations we analysed appear to be consistent with a radial pulsation (the dominant pulsation mode is the first overtone) yielding shock waves which propagate throughout the atmosphere and generate a complex, asynchronous motion of the outer layers.