€Zwaan & Verbunt suggested that at 3hr the magnetic braking switches
off, because secondaries with this mass are fully convective, so
stellar dynamo is quenched
€Mass transfer rate then is reduced, so secondary falls
away from
Roche Lobe, and mass transfer stops, so these systems are not seen as
CVs
€Then gravitational radiation would continue to operate,
slowly driving
the two stars together, until contact with the Roche Lobe was
reestablished and accretion restarted: the origin of the <2hr
binaries
€While this has been the ³standard² explanation for some time, questions
have always remained about the real effect of fully convective secondaries on
the generation of magnetic field by the dynamo
€Some evidence for this mechanism clear from the absence of
a
significant gap in the magnetic systems, in which braking is affected by the
field from the primary (in addition to that from the secondary)