On resonant and non-resonant origin of double-mode Cepheid pulsation

Double-mode Cepheid behaviour may arise either from non-resonant or resonant mode interaction. Inclusion of turbulent convection into pulsation codes by Kolláth et al. led to stable double-mode F+1O Cepheid pulsation [1]. However, our recent computations indicate, that these models resulted from incorrect neglect of negative buoyancy effects [2]. Once these effects are taken into account, only some resonant double-mode models could be found. These models do not solve the puzzle of double-mode phenomenon, as they are restricted to narrow parameter ranges. For majority of the observed double-mode Cepheids non-resonant mechanism has to be operational.