One of the controversies surrounding the detection of exoplanets around post-common envelope binaries is the possibility that the orbital period variations observed might be the result of the Applegate mechanism as opposed to reflex motion from an orbiting planet.
Would these concerns also apply to AM CVn systems or other close white dwarf+white dwarf binaries? The Applegate mechanism itself is explained in terms of the activity cycle of the main sequence component of a cataclysmic variable, could a similar mechanism operate or would the changes in the quadrupole moment of the star be too small to produce observable effects?
