The space motions and luminosity function of white dwarf.
Abstract
An analysis is presented of the kinematics and number-absolute-magnitude distributions for an enlarged sample of 424 spectroscopically identified white dwarfs that have both proper motions and colors. Space velocities and associated statistics are compared for subsets of DA and non-DA white dwarfs, chosen in an attempt to minimize the selection effects on their original discovery. The DB white dwarfs do not differ kinematically from the DA stars in the same luminosity or color range; no significant differences between the groups are found, with the exception of the higher-velocity C2 (A4670) stars. Our results seem consistent with the hypothesis that DA and non-DA stars evolve from similar, broad progenitor mass ranges and that both represent an admixture of stellar populations. Most magnetic white dwarfs exhibit rather small space velocities. The number-absolute-magnitude distributions of the DA and non-DA stars are also compared. There are relatively fewer hot non-DA (DO) stars and more cool non-DA stars. However, these apparent differences between the samples may be explainable in terms of uncertainties in the magnitude calibrations and selection effects in the spectral classification. The true luminosity function for the entire sample is estimated, using completeness arguments. The resulting distribution lends no support to the belief that there is a deficit of cool white dwarfs to Mv < 15.5. The distribution is consistent, however, with recent cooling theory-evolutionary calculations. Subject headings: stars: evolution - stars: stellar dynamics - stars: stellar statistics - stars: white dwarfs
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1977
- DOI:
- 10.1086/155178
- Bibcode:
- 1977ApJ...213..468S