Non-linear modelling of beat Cepheids: resonant and non-resonant models

Context. Double-periodic (beat) Cepheids are important astrophysical objects which allow testing both the stellar evolution and stellar pulsation theories, as well as the physical properties of matter in stellar conditions. However, the phenomenon of double-periodic pulsation is still poorly understood. Recently we rediscussed the problem of modelling the double-periodic pulsation with non-linear hydrocodes. We showed that the published non-resonant double-mode models are incorrect, because they exclude the negative buoyancy effects.