The period changes of algol type eclipsing binaries

In the present thesis the period changes and the causes of these changes of Algol type eclipsing binary systems were studied. In order to understand the period changes of Algol type binaries with and without mass transfer, the O-C diagrams formed by the observed minima times of selected 157 Algol type binaries were studied in the firs stage of the present thesis. The observed data of selected binaries contain at least 25 minima times distributed at least 25 years time interval. The O-C diagrams which were base for the analysis were given as a catalogue in the appendix to the thesis. As a second stage of the thesis, three systems, V819 Her, QS Aql and VX Lac, selected from catalogue were studied in detail on the new observational data. New light curves were obtained at ÇOMÜ Observatory and analyzed together with other data from the literature for the absolute dimentions of the systems. Algol type eclipsing binary systems, V819 Her and QS Aql are a component of MCA 47 and KUI 93 visual double star systems, respectively. The orbital period changes and astrometric data of V819 Her and QS Aql were analized simultaneously. The results of these analyses were presented that the orbital period changes of this systems are caused by the other visual components of MCA 47 and KUI 93. The third light contributions of each three systems obtained by the analysis of light curves support the third components which suggested from O-C analyzes. Thus, the third bodies of three systems V819 Her, QS Aql and VX Lac supported with different ways, in general, the reliability of interpretations of third body on O-C diagrams strengthens.