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The class of Double Period Variables (DPVs) consists of close interactingbinaries, with a characteristic long period that is an order of magnitudelonger than the corresponding orbital period, many of them with acharacteristic ratio of about 3.5x10^1. We consider here the possibility thatthe accretion flow is modulated as a result of a magnetic dynamo cycle. Due tothe short binary separations, we expect the rotation of the donor star to besynchronized with the rotation of the binary due to tidal locking. We herepresent a model to estimate the dynamo number and the resulting relationbetween the activity cycle length and the orbital period, as well as anestimate for the modulation of the mass transfer rate. The latter is based onApplegate's scenario, implying cyclic changes in the radius of the donor starand thus in the mass transfer rate as a result of magnetic activity. Our modelis applied to a sample of 17 systems with known physical parameters, 10 alsowith known orbital periods. In spite of the uncertainties of our simplifiedframework, the results show a reasonable agreement, indicating that a dynamointerpretation is potentially feasible. At the same time, we note that theorbital period variations resulting from Applegate's model are sufficientlysmall to be consistent with the data. We conclude that both larger samples withknown physical parameters as well as potential direct probes of the magnetismof the donor star, including cold spots as well as polarization, will bevaluable to further constrain the nature of these systems.

A dynamo mechanism as the potential origin of the long cycle in Double Periodic Variables