Program: GN-2009A-Q-256

White dwarf, neutron star, and black hole binaries make up a wide variety of objects, including e.g. SNIa progenitors and X-ray binaries. Binary population studies of these objects suffer from poor understanding of the common envelope (CE) phase and subsequent orbital angular momentum loss, and from uncertainties in the initial mass ratio and orbital separation distributions. Significant progress in our understanding of compact binary evolution depends on novel observational input that will constrain and calibrate the models. White-dwarf plus main-sequence binaries are a prolific and intrinsically simple type of systems that are well-suited tracers of binary evolution. Our observations indicate that the fraction of WDMS binaries that underwent a CE phase is rising towards lower companion star masses, which contrasts the predictions and suggests that standard assumptions about the CE ejection efficiency and/or initial binary separation are wrong. This is the second (and last) request for Gemini time to consolidate our finding by extending the mass range of our sample.