Effect of Tidal Torques on Rotational Mixing in Close Binaries**Supported by the National Natural Science Foundation of China under Grant No 11463002, and the Open Foundation of key Laboratory for the Structure and evolution of Celestial Objects of Chinese Academy of Sciences under Grant No OP201405.

Abstract

The effect of tidal torques on rotational mixing in close binaries is investigated. It is found that spin angular momentum can attain a high value due to a strong tidal torque. Nitrogen and helium enrichment occurs early in the binary system that is triggered by tides. The stellar radius can reach a high value in the single star model with high initial velocities at the early stage of the evolution, but efficient rotational mixing can inhibit stellar expanding at the subsequent evolution. Central compactness is increased by the centrifugal force at the early stage of evolution but is reduced by rotational mixing induced by strong tides. The binary models with weak tides have high values of central temperature and stellar radius. Rotational mixing in single stars can slow down the shrinkage of convective cores, while convective cores can be expanded by strong tides in the binary system. Efficient rotational mixing induced by tides can cause the star to evolve towards high temperature and luminosity.