EKMAN PUMPING AND TIDAL DISSIPATION IN CLOSE BINARIES - A REFUTATION OF TASSOULS MECHANISM

We show that the existence of an Ekman boundary layer does not enhance the tidal dissipation in a close binary star because the tides do not exert a stress on the stellar surface. The synchronization time-scale is of order (epsilon(T))(-2)t(adj), where t(adj) is the (global) visc ous damping time and epsilon(T) is the tidal deformation caused by the companion (Darwin 1879; Zahn 1966; Scharlemann 1982; Rieutord & Bonaz zola 1987). We thus refute the claim made by Tassoul (1987), who thoug ht to have found a very efficient mechanism for the synchronization an d circularization of binary systems. We analyze the paper by Tassoul & Tassoul (1992b) and prove that the alleged magnitude of their Ekman p umping is due to an improper treatment of the surface boundary conditi ons. Their mechanism would have dramatic, yet unverified consequences, as illustrated by two examples of tidal interaction: between Io and J upiter, and in the newly discovered planetary system 51 Peg.