Magnetic activity, tides, and orbital period changes in close binaries

Abstract

It is proposed that a variable quadrupole moment produced by magnetic activity in the outer convection zone of one of the stars in a close binary is responsible for the orbital period changes which occur on a time scale of order 10 yr. In the model, magnetic activity modulates the orbital period, superposed on any long-term period changes that may occur. The model predicts that the orbital period changes should be periodic with the period of the activity cycle. If the period changes due to secular angular momentum loss and magnetic activity can be separated, a powerful new probe of stellar magnetic activity will emerge, tidal synchronization theory can be tested, and the progenitor population and evolution rate of cataclysmic variables can be determined.