A new method for judging the synchronous rotation of binary stars.

The present paper suggests a new method for judging the synchronous rotation of binary stars. The ratio of the theoretical apsidal period for the assumed synchronous binary to the observed value of the same star is used as a synchronous parameter to judge the synchronization of binary stars. The status of synchronization for Y Cyg and CW Cep are judged by using this new method. It is shown that Y Cyg is a near-synchronous binary and CW Cep is a synchronous binary. The result obtained by this method is in agreement with those by other authors.