Ultraviolet-excess sources with a red/infrared counterpart : Low-mass companions, debris discs and QSO selection

We present the result of the cross-matching between ultraviolet (UV)-excess sources selected from the UV-Excess Survey of the Northern Galactic Plane (UVEX) and several infrared (IR) surveys (2MASS, UKIDSS and WISE). From the position in the (J - H) versus (H - K) colour-colour diagram, we select UV-excess candidate white dwarfs with an M-dwarf type companion, candidates that might have a lower mass, brown-dwarf type companion and candidates showing an IR-excess only in the K band, which might be due to a debris disc. Grids of reddened DA+dM and sdO+MS/sdB+MS model spectra are fitted to the U, g, r, i, z, J, H, K photometry in order to determine spectral types and estimate temperatures and reddening. From a sample of 964 hot candidate white dwarfs with (g - r)