Özet:

The long-term period variations of the classical algol-type binaries XZ And, U Cep, b Per, RT Per, ST Per and TX UMa were studied by using all available observed times of eclipse minima. The (O-C) diagrams formed by the times of eclipse minima were found to be representable by one or more cyclic variations superimposed on a secular parabolic variation. The secular variations in the orbital periods should be caused by the mass transfer between the component stars and the mass loss from the systems. For our sample of Algol systems, none of the cyclic variations were found caused by the apsidal motion. The cyclic variations were interpreted in terms of the cyclic magnetic activity effect of the late-type secondaries and/or the light-time effect due to additional unseen component stars around the systems.

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