Double-periodic blue variables in the Magellanic Clouds

We report the discovery, based on an inspection of the OGLE-II database, of a group of blue variables in the Magellanic Clouds showing simultaneously two kinds of photometric variability: a short-term cyclic variability with typical amplitude Delta I ~ 0.05 mag and period P₁ between 4 and 16 days and a sinusoidal, long-term cyclic oscillation with much larger amplitude Delta I ~ 0.2 mag with period P₂ in the range of 150-1000 days. We find that both periods seems to be coupled through the relationship P₂ = 35.2 +/- 0.8 P₁. In general, the short term variability is reminiscent of those shown by Algol-type binaries. We propose that the long-term oscillation could arise in the precession of a elliptical disc fed by a Roche-lobe filling companion in a low mass ratio Algol system.