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

TL;DR

This study presents spectroscopic follow-up of 132 UV-excess objects from the UVEX survey, classifying their populations and analyzing their properties, revealing a high proportion of genuine UV-excess sources including white dwarfs and subdwarfs.

Contribution

First spectroscopic follow-up of UVEX UV-excess candidates providing detailed classifications and population analysis, enhancing understanding of their distribution and properties.

Findings

95% of candidates are genuine UV-excess sources

47% of white dwarfs are DA type with low reddening

White dwarfs are more common at fainter magnitudes and lower Galactic latitudes

Abstract

We present the results of the first spectroscopic follow-up of 132 optically blue 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 fit to determine spectral types, temperatures, surface gravities and reddening. From this initial spectroscopic follow-up 95% of the UV-excess candidates turn out to be genuine UV-excess sources such as white dwarfs, white dwarf binaries, subdwarfs type O and B, emission line stars and QSOs. 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% with reddening smaller than E(B-V)<0.7 mag. Relations between the different populations and their UVEX photometry, Galac- tic 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.