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The Sloan Digital Sky Survey turned out to be very efficient in identifyingwhite dwarf/main sequence binaries (WDMS). The population of WDMS systemsconsists of wide systems whose stellar components evolve like single stars and- more interesting in the context of close binary evolution - PCEBs. We pursuea large-scale follow-up survey to identify and characterise the PCEBs among theWDMS binaries that have been found with SDSS. We use a two-step strategy withthe identification of PCEBs among WDMS in the first and orbital perioddeterminations in the second phase. Here we present first results of ourVLT/FORS2 pilot-study that has the target of identifying the PCEBs among thefainter (g>~18.5) SDSS-WDMS. From published SDSS catalogues we selected 26 WDMStargets to be observed with VLT/FORS2. Using a spectral decomposition/fittingtechnique we determined the white dwarf effective temperatures and surfacegravities, masses, and secondary star spectral types for all WDMS in oursample. We used the NaI 8183.27,8194.81 doublet to measure radial velocityvariations of our targets and performed additional follow-up spectroscopy usingMagellan-Clay/LDSS3 of two systems showing significant radial velocityvariations. Among the 26 WDMS systems we find 9 strong PCEB candidates showingclear (>=3sigma) radial velocity variations and we estimate the fraction ofPCEBs among SDSS WDMS to be ~35%. We find indications for a dependence of therelative number of PCEBs among SDSS-WDMS on the spectral type of the secondarystar. These results are subject to small number statistics and need to beconfirmed by additional observations. For two of the identified PCEBcandidates, SDSSJ1047+0523 and SDSSJ1414-0132, we measured the orbital periodsto be 9.17hrs and 17.48hrs respectively.

Post common envelope binaries from SDSS. II: Identification of 9 close binaries with VLT/FORS2