A close binary containing a magnetic white dwarf and a lower main-sequence secondary evolves through several stages following the onset of mass transfer. Whether the initial rotation period is greater or less than P(eq), the equilibrium period for disk accretion, the rotation period approaches P(eq) on a time scale of not greater than about 100-million yr, and the system becomes a DQ Her binary. Further evolution is due to angular momentum losses caused by gravitational radiation and magnetic braking of the secondary. As the orbital separation and luminosity decrease, the magnetosphere of the white dwarf encounters the secondary, if B is greater than about 3,000,000 gauss, and synchronizes the rotation of the white dwarf as in the AM Her binaries. The present model is consistent with the observation that most DQ Her binaries have P(orb) greater than 3 hr, while most AM Her binaries have P(orb) less than 2 hr.
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Chanmugam et al. (1984) studied this question.