The orbits of subdwarf B + main-sequence binaries

Context. The predicted orbital period histogram of a subdwarf B (sdB) population is bimodal with a peak at short (250 days) periods. Observationally, however, there are many short-period sdB systems known, but only very few long-period sdB binaries are identified. As these predictions are based on poorly understood binary interaction processes, it is of prime importance to confront the predictions to well constrained observational data. We therefore initiated a monitoring program to find and characterize long-period sdB stars.