Synchronization and circularization in early-type binaries on main sequence

We showed in a preceding paper based on an analysis of the observed rates of apsidal motion that synchronization in early-type eclipsing binaries continues on the main sequence, and the observed synchronization times, <it>t</it><inf>syn</inf>, agree with the Zahn's theory and are inconsistent with the shorter time-scale proposed by Tassoul. It follows from this that circularization in early-type binaries must also proceed in accordance with the Zahn's theory because the circularization times, <it>t</it><inf>circ</inf>, in both theories are rather tightly related to <it>t</it><inf>syn</inf> via relation <it>t</it><inf>circ</inf>≈ α<it>t</it><inf>syn</inf>, where α is the orbital-to-axial momentum ratio. To further investigate this problem, we compile a catalogue of 101 eclipsing binaries with early-type main-sequence components (<it>M</it><inf>1,2</inf> > 1.6 M<inf>⊙</inf>). We determine the ages, <it>t</it>, and circularization time-scales, <it>t</it><inf>circ</inf>, for all these systems in terms of the two competing theories by comparing observational data with modern models of stellar evolution of Claret and atmospheric models of Kurucz. We compute <it>t</it><inf>circ</inf> with the allowance for the evolutionary variations of the physical parameters of the components and, for the first time in such studies, also take into account the variations of the orbital parameters (<it>P</it>, <it>a</it>, <it>e</it>) in the process of circularization subject to the conservation of the total angular momentum. The results of these computations show that the mechanism of orbital circularization in early-type close binary systems (CBSs) suggested by Tassoul is, like in the case of synchronization, inconsistent with observational data. At the same time, the Zahn's mechanism, which is based on the dissipation of the energy of dynamic tides in the upper layers of the envelopes of CBSs components due to non-adiabaticity of these layers, agrees satisfactorily with observations.