Understanding white dwarf binary evolution with white dwarf/main\n sequence binaries: first results from SEGUE

Close white dwarf binaries make up a wide variety of objects such as double\nwhite dwarf binaries, which are possible SN Ia progenitors, cataclysmic\nvariables, super soft sources, or AM CVn stars. The evolution and formation of\nclose white dwarf binaries crucially depends on the rate at which angular\nmomentum is extracted from the binary orbit. The two most important sources of\nangular momentum loss are the common envelope phase and magnetic braking. Both\nprocesses are so far poorly understood. Observational population studies of\nwhite dwarf/main sequence binaries provide the potential to significantly\nprogress with this situation and to clearly constrain magnetic braking and the\nCE-phase. However, the current population of white dwarf/main sequence binaries\nis highly incomplete and heavily biased towards young systems containing hot\nwhite dwarfs. The SDSSII/SEGUE collaboration awarded us with 5 fibers per plate\npair in order to fill this gap and to identify the required unbiased sample of\nold white dwarf/main sequence binaries. The success rate of our selection\ncriteria exceeds 65% and during the first 10 months we have identified 41 new\nsystems, most of them belonging to the missed old population.\n