Context : A number of binary systems present evidence of enhanced activity around periastron passage , suggesting a connection between tidal interactions and these periastron effects .

Aims : The aim of this investigation is to study the time-dependent response of a star ’ s surface as it is perturbed by a binary companion .
Here we focus on the tidal shear energy dissipation .

Methods : We derive a mathematical expression for computing the rate of dissipation , \dot { E } , of the kinetic energy by the viscous flows that are driven by tidal interactions on the surface layer of a binary star .
The method is tested by comparing the results from a grid of model calculations with the analytical predictions of Hut ( 1981 ) and the synchronization timescales of Zahn ( 1977 , 2008 ) .

Results : Our results for the dependence of the average ( over orbital cycle ) energy dissipation , \dot { E } _ { ave } , on orbital separation are consistent with those of Hut ( 1981 ) for model binaries with an orbital separation at periastron r _ { per } / R _ { 1 } \gtrsim 8 , where R _ { 1 } is the stellar radius .
The model also reproduces the predicted pseudo-synchronization angular velocity for moderate eccentricities ( e \leq 0.3 ) .
In addition , for circular orbits our approach yields the same scaling of synchronization timescales with orbital separation as given by Zahn ( 1977 , 2008 ) for convective envelopes .
The computations give the distribution of \dot { E } over the stellar surface , and show that it is generally concentrated at the equatorial latitude , with maxima generally located around four clearly defined longitudes , corresponding to the fastest azimuthal velocity perturbations .
Maximum amplitudes occur around periastron passage or slightly thereafter for supersynchronously rotating stars .
In very eccentric binaries , the distribution of \dot { E } over the surface changes significantly as a function of orbital phase , with small spatial structures appearing after periastron .
An exploratory calculation for a highly eccentric binary system with parameters similar to those of \delta Sco ( e =0.94 , P =3944.7 d ) indicates that \dot { E } _ { ave } changes by \sim 5 orders of magnitude over the 82 days before periastron , suggesting that the sudden and large amplitude variations in surface properties around periastron may , indeed , contribute toward the activity observed around this orbital phase .

Conclusions :