On the orbital circularization of close binaries

A modified approach to the tidal circularization of short-period binaries with convective envelopes is suggested. The proposed model is based on Zahn's (1966) theory and is motivated by his recent comment about the reduction of stellar viscosity due to the fact that the tidal variation time scale is comparable to, or shorter than, the typical convection turnover time scale. In the modified approximation the circularization time scale for close binaries is proportional to the binary period to the power of 10/3. This exponent is smaller than in previously suggested theories. The presently available data, though admittedly sparse, are compared with the different approximations. The new exponent seems to fit the data better than those of the previous theories.