€The white dwarf in CVs is the relic of the more massive
star in the binary, already past a giant phase
€The secondary star will have spent some time in the
envelope of the primary red giant perhaps accreting material
from it
€Dynamical friction reduces the separation of the remnant
core of the primary and the secondary, causing the secondary
to spiral inwards and perhaps contributing to the ejection
of the envelope
€After this phase have a detached hot white dwarf with a
main sequence secondary; such stars are known (eg BE
UMa) and show strong reflection effects from the hot primary illuminating the secondary
€Further angular momentum losses can shrink the binary separation until the secondary comes into contact with
its Roche lobe, and mass transfer starts, giving rise to a
CV
€Alternatively in longer period systems the secondary can evolve, increasing in size and filling its Roche
lobe