  White dwarf (WD) stars are often associated with the central stars of
planetary nebulae (CSPNe) on their way to the cooling track. A large number of
WD star candidates have been identified thanks to optical large-scale surveys
such as Gaia DR2 and EDR3. However, hot-WD/CSPNe stars are quite elusive in
optical bands due to their high temperatures and low optical luminosities. The
Galaxy Evolution Explorer (GALEX) matched with the INT Galactic Plane Survey
(IGAPS) allowed us to identify hot-WD candidates by combining the GALEX far-UV
(FUV) and near-UV (NUV) with optical photometric bands (g, r, i and H$\alpha$).
After accounting for source confusion and filtering bad photometric data, a
total of 236485 sources were found in the GALEX and IGAPS footprint (GaPHAS). A
preliminary selection of hot stellar sources was made using the GALEX colour
cut on FUV-NUV>-0.53, yielding 74 hot-WD candidates. We analysed their spectral
energy distribution (SED) by developing a fitting program for single- and
two-body SED using an MCMC algorithm; 41 are probably binary systems (a binary
fraction of ~55% was estimated). Additionally, we classified the WD star
candidates using different infrared (IR) colours available for our sample
obtaining similar results as in the SED analysis for the single and binary
systems. This supports the strength of the fitting method and the advantages of
the combination of GALEX UV with optical photometry. Ground-based time-series
photometry and spectra are required in order to confirm the nature of the WD
star candidates.
