On the masses and the evolution of cataclysmic binaries

Masses of cataclysmic binaries (CB's) are derived from observational data (published earlier) and a theoretical relation between the secondary's mass and the period. It is found that the mass ratios of CB's having a relatively massive main sequence secondary (i.e. M2 > approximately 0.9 mass of the sun, corresponding to periods larger than about 7 hr) are not far from being unity. The assumption of a mass ratio near to unity throughout for CB's removes the discrepancy between the mean mass of single white dwarfs and the mean mass of white dwarfs in CB's. A lower limit for the mass ratios of long-living systems (being less than, but near to unity) is found from the discussion of the stability against mass exchange. An evolutionary scheme for CB's based on present stellar evolution theories is sketched. According to this scheme, WUMa systems have probably to be excluded as possible progenitors of CB's. However, the typical configuration of a CB could easily be understood as the result of an evolution of type C of a close binary undergoing mass exchange during the primary's red giant phase, connected with substantial losses of mass and angular momentum from the system. (author)