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