Spectroscopic follow-up of ultraviolet-excess objects selected from the UVEX survey

Abstract

We present the results of the first spectroscopic follow-up of 132 optically blue ultraviolet (UV)-excess sources selected from the UV-Excess Survey of the Northern Galactic Plane (UVEX). The UV-excess spectra are classified into different populations and grids of model spectra are fitted to determine spectral types, temperatures, surface gravities and reddening. From this initial spectroscopic follow-up 95 per cent of the UV-excess candidates turn out to be genuine UV-excess sources such as white dwarfs, white dwarf binaries, subdwarf types O and B, emission-line stars and quasi stellar objects. The remaining sources are classified as slightly reddened main-sequence stars with spectral types later than A0V. The fraction of DA white dwarfs is 47 per cent with reddening smaller than E(B - V) ≤ 0.7mag. Relations between the different populations and their UVEX photometry, Galactic latitude and reddening are shown. A larger fraction of UVEX white dwarfs is found at magnitudes fainter than g > 17 and Galactic latitude smaller than |b| <4 compared to main-sequence stars, blue horizontal branch stars and subdwarfs.