On evolutionary processes in close binary stars

In this thesis, we investigate evolutionary status and processes of contact binaries. Essential property of these systems is that both components of the system fill or even overfill their inner Roche lobe. Owing to separation of components is so close, gravitational interactions between components are enhanced. For this reason mass transfer may occur from one to the other component. As a result of this mass transfer, while secondary components are much more luminous according to their mass, primary components look like typical main sequence stars. Mass of a star is a major parameter that is governing evolution of the star. In case of close binary system, initial mass ratio is fundamental parameter that effects orbital evolution. Thus, determining of initial masses of components of contact binaries is crucial for understanding of evolutionary processes of these systems. Within the thesis, for the first time, we have computed initial masses of secondary components of contact binaries using observable physical properties of the system's components. Amount of mass loss from contact binaries has been investigated using models based on conceivable various scenarios. Consequently, we have asserted that division of contact binaries as A and W subtypes is determined by the initial masses of the secondary components. Also we have deduced the initial masses of primary components, detailed information about evolutionary process and formation of the contact binaries.