Mode Identification with Cepheid Phase-lag

A large model survey with the Florida-Budapest hydrodynamical code has revisited the Cepheid phase-lag problem. A good agreement between the models and the available observational data has been found for normal amplitude Cepheids. The phase-lag is a method for mode identification that is complementary to that of Fourier decomposition coefficients. In this contribution we exploit its potential in identifying the pulsational mode of Cepheids. The possible application of the phase lag as a test for ultra-low amplitude pulsation is discussed as well.