Double Mode Cepheids with Amplitude Modulation
  Recent search for multiperiodicity in LMC Cepheids (Moskalik, Kolaczkowski & Mizerski 2004) has led to discovery of periodic modulation of amplitudes and phases in many of the first/second overtone (FO/SO) double mode pulsators. We discuss observational characteristics and possible mechanisms responsible for this behaviour. 
P. Moskalik, Z. Kolaczkowski and T. Mizerski