Orbital Evolution of Algol Binaries with a Circumbinary Disk

It is generally thought that conservative mass transfer in Algol binariescauses their orbits to be wider, in which the less massive star overflows itsRoche-lobe. The observed decrease in the orbital periods of some Algol binariessuggests orbital angular momentum loss during the binary evolution, and themagnetic braking mechanism is often invoked to explain the observed orbitalshrinkage. Here we suggest an alternative explanation, assuming that a smallfraction of the transferred mass forms a circumbinary disk, which extractsorbital angular momentum from the binary through tidal torques. We also performnumerical calculations of the evolution of Algol binaries with typical initialmasses and orbital periods. The results indicate that, for reasonable inputparameters, the circumbinary disk can significantly influence the orbitalevolution, and cause the orbit to shrink on a sufficiently long timescale.Rapid mass transfer in Algol binaries with low mass ratios can also beaccounted for in this scenario.Comment: 9 pages, 5 figures, accepted for publication in Ap