WR BINARIES - THEORETICAL ASPECTS

The different channels for the formation of WR-stars, as suggested in the literature, are investigated. The presently available tools, in terms of evolutionary recipies, are reviewed and the results investigated of the use of these tools, with respect to the WR-binaries. Two of the three basic formation channels, mentioned in the literature, may serve as ways to obtain the presently observed group of WR-binaries: stellar wind mass loss in O-stars during the pre-WR phase and mass transfer in a massive close binary system. Discrepancies with observations necessitated the incorporation of stellar wind in the binary scenario. Theoretical developments in the last years are reviewed and confronted with the observations. The necessity of mass transfer in the formation process is argued for a major fraction of the double-lined WR-binaries. Using specific evolutionary ingredients, the original parameters of the systems are calculated. We also discuss the appearance and disappearance of double-lined WR-systems as well as the existence of eccentric WR-systems after mass transfer. The evolution of a number of specific systems is discussed individually.