A determination of the space density and birth rate of hydrogen-line (DA) white dwarfs in the Galactic plane, based on the UVEX survey

Abstract

We present a determination of the average space density and birth rate of\nhydrogen-line (DA) white dwarfs within a radius of 1 kpc around the Sun, based\non an observational sample of 360 candidate white dwarfs with g<19.5 and\n(g-r)<0.4, selected from the UV-excess Survey of the Northern Galactic Plane\n(UVEX), in combination with a theoretical white dwarf population that has been\nconstructed to simulate the observations, including the effects of reddening\nand observational selection effects. The main uncertainty in the derivation of\nthe white dwarf space density and current birth rate lies in the absolute\nphotometric calibration and the photometric scatter of the observational data,\nwhich influences the classification method on colours, the completeness and the\npollution. Corrections for these effects are applied. We derive an average\nspace density of hydrogen-line (DA) white dwarfs with T_eff > 10,000K\n(M_V<12.2) of (3.8 +/- 1.1) x 1e-4 pc^-3, and an average DA white dwarf birth\nrate over the last 7e7 years of (5.4 + 1.5) x 1e-13 pc^-3 yr^-1. Additionally,\nwe show that many estimates of the white dwarf space density from different\nstudies are consistent with each other, and with our determination here.\n