The CV period gap : still there

We consider a recently–proposed alternative explanation of the CV period gap in terms of a revised mass–radius relation for the lower main sequence. We show that no such thermal–equilibrium relation is likely to produce a true gap. Using population synthesis techniques we calculate a model population that obeys the claimed equilibrium mass–radius relation. A theoretical period histogram obtained from this population shows two prominent period spikes rather than a gap. We consider also recent arguments suggesting that the period gap itself may not be real. We argue that, far from demonstrating a weakness of the interrupted–braking picture, the fact that most CV subtypes prefer one side of the gap or the other is actually an expected consequence of it.