Evolution
(ctd)
€Transfer of material from a lower mass star to a higher
mass star (as in a CV) causes the orbital separation to
increase, lengthening the period and causing the star to fall
away from contact with its Roche Lobe and accretion to stop
€Hence some other mechanism has to been in place for stable
mass transfer
€Main candidate for more than two decades has been the magnetic braking
caused by wind material from the secondary being threaded by field lines to large
distances (Zwaan & Verbunt)
€This magnetic braking robs the binary of angular momentum,
so the two stars move closer together, maintaining
contact with the Roche Lobe and quasi-stable mass transfer
€From this an expected population of CVs can be generated
as a function of orbital period, given ages and mass
transfer rates