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Tidal and rotational effects in the perturbations of hierarchical triple stellar systems

Abstract
Close hierarchical triple stellar systems offer a unique possibility to study not only theoretically, but even observationally (at least with limitations) the interaction between a non-spherical and temporally variable gravitational field and the internal structures of the stars. From this purpose a new numerical integrator was developed for studying the orbital and spin evolution of hierarchical triple stellar systems. The code includes equilibrium tide approximations with arbitrary direction of rotational axes. The variation of the orbital elements (e.g. the inclination of the close -eclipsing- binary) and its observational consequences according to the distorted models with different mass-distributions of the stars, as well as with and without dissipation, is studied in the case of the well-known eclipsing triple system Algol. We found that in the absence of dissipation the third star may cause sudden fluctuations in the orbital elements and in the rotation of the binary components, even if they were previously synchronized. Tidal dissipation can eliminate these fluctuations; nevertheless certain variations may subsist, and they could explain some effects that have been observed in several eclipsing binaries.