Synchronization timescales for three solar-type stars that have Jupiter-mass companions in short-period orbits

We examine the physical properties of the three currently known star-plus-planet systems that have orbital periods of similar to 3-5 days (51 Peg, nu And, and tau Boo). The observed properties are, in general, more consistent with the Zahn viscous dissipation mechanism than with the Tassoul hydrodynamic spin-down mechanism (at least in the latter's present formulation). However, a comparison of the data for tau Boo with the Zahn theory suggests that the predicted synchronization timescale t(z) might be regarded as an upper limit to the actual time needed to synchronize the outer convective layers, and that the latter may actually be shorter than t(z) by a factor of greater than or equal to 3.