OB-TYPE BINARIES - MODELS VERSUS OBSERVATIONS

Recently published models on close binary evolution for massive stars (M > 5M.) are compared to a set of detached and semidetached OB binari es. For the majority of the detached systems, we find good corresponde nce between theoretical and observed characteristics for stars with ma sses between 4.5M. and 17M.. We explore the origin of semidetached sys tems, and discuss anomalies between models and observed characteristic s. An initial mass ratio of around 0.6 seems to be preferred for this group. Finally, we briefly examine a number of massive (marginal) cont act systems. The latter systems all seem to evolve according to case A of mass transfer.