On synchronization and circularization in close binary systems

In the present presentation, we discuss the synchronism and circularism in 81 detached close binary systems. We find that Zahn's theories on synchronization and orbital circularization of binaries are compatible with observational data for the overwhelming majority of our samples. However, we also note that Zahn's theories alone seem to have difficulties to explain the high degree of synchronism and circularism in binaries with abnormal metallic abundance (Am and Fm stars), and that to understand the circular orbits of four systems whose both components have not been synchronized yet. Perhaps, studies on the orbital circularization of pre-main-sequence binary systems and on magnetic baking cloud provide some clues for the problems.