5 Conclusion

Recent observations confirm the two-frequencies solution for DQ Cephei, and the observations indicating the two pulsation modes show possible regular amplitude variations with a period exceeding 46 years. The amplitude variations seem to indicate energy conservation. The modulation period of the amplitude variations is too long to be explained by beat modulation of rotating split, and the position of DQ Cephei on HR diagram does not agree well with the hypothesis that the modulation of amplitude variation is caused by the overlap of different modes. So an interpretation in terms of two or more close frequencies can be ruled out. We suggest that the amplitude variation is caused by some kind of intrinsic amplitude variability, such as a slow transfer of pulsation energy between different modes.

Acknowledgements

This work has been supported by the Chinese National Natural Science Foundation