A study of the white dwarf luminosity function

The dependence of white dwarf luminosity functions on the assumed age of the Galactic disk is examined, taking into account the relationship between white dwarf mass and progenitor mass, the progenitor lifetime, the mass dependence of cooling curves, and possible variations in the birthrate function in the past. At low luminosities, the resultant distribution in number versus luminosity depends very strongly not only on the shape of the cooling curves for different masses, but also on the spectrum of white dwarf masses that contribute to the distribution. For an age of about 9 Gyr, it is suggested that at luminosities only a quarter of a magnitude fainter than the dimmest white dwarfs yet found, the space density of white dwarfs is larger by a factor of 10 than the space density which the Winget et al. (1987) luminosity function suggests.