  The spectroscopic catalogue of white dwarf-main sequence (WDMS) binaries from
the Sloan Digital Sky Survey (SDSS) is the largest and most homogeneous sample
of compact binary stars currently known. However, because of selection effects,
the current sample is strongly biased against systems containing cool white
dwarfs and/or early type companions, which are predicted to dominate the
intrinsic population. In this study we present colour selection criteria that
combines optical (ugriz DR8 SDSS) plus infrared (yjhk DR9 UKIRT Infrared Sky
Survey (UKIDSS), JHK Two Micron All Sky Survey (2MASS) and/or w1w2 Wide-Field
Infrared Survey Explorer (WISE)) magnitudes to select 3419 photometric
candidates of harbouring cool white dwarfs and/or dominant (M dwarf)
companions. We demonstrate that 84 per cent of our selected candidates are very
likely genuine WDMS binaries, and that the white dwarf effective temperatures
and secondary star spectral types of 71 per cent of our selected sources are
expected to be below <~10000-15000K, and concentrated at ~M2-3, respectively.
We also present an updated version of the spectroscopic SDSS WDMS binary
catalogue, which incorporates 47 new systems from SDSS DR8. The bulk of the DR8
spectroscopy is made up of main-sequence stars and red giants that were
targeted as part of the Sloan Extension for Galactic Understanding and
Exploration (SEGUE) Survey, therefore the number of new spectroscopic WDMS
binaries in DR8 is very small compared to previous SDSS data releases. Despite
their low number, DR8 WDMS binaries are found to be dominated by systems
containing cool white dwarfs and therefore represent an important addition to
the spectroscopic sample. The updated SDSS DR8 spectroscopic catalogue of WDMS
binaries consists of 2316 systems.
