White dwarfs in wide binaries and the age of the Galaxy

A comprehensive study of common proper binary systems suspected of containing white dwarf stars is being conducted by Oswalt and collaborators (Oswalt et al. 1988). These systems usually contain a white dwarf and a main sequence star. In the present study, we use the white dwarf luminosity function to determine the age of the local Galactic disk as well as the local space density of white dwarfs. We obtained BVRI photometry of approximately 475 systems (of 512) which were found to contain about 325 white dwarfs. Of these white dwarfs, 152 met the selection criteria for our study and were used in the final analysis.; Using this largest sample of cool white dwarfs in binary systems observed to date, we have determined an age for the Galactic disk of 9.7{dollar}sbsp{lcub}-0.8{rcub}{lcub}+0.9{rcub}{dollar} Gyr which yields a lower limit age for the Universe of about 11.7 Gyr. Recent globular cluster studies agree to within {dollar}pm{dollar}1{dollar}sigma{dollar} for the Galaxy age derived from our Disk age. The latest cosmologically derived age for the Universe, modified for the recently released Hipparcos data, is now in accordance with our age estimates for the Universe, for H{dollar}sb{lcub}rm o{rcub}{dollar} (69 km s{dollar}sp{lcub}-1{rcub}{dollar} Mpc{dollar}sp{lcub}-1{rcub}{dollar}) and an inflationary cosmology. Further, our age is in accord with the ages derived for the Galaxy from nucleocomsochronology and meteoritic sample analyses. As a part of this work, we have determined the white dwarf space density to be 4.5 {dollar}pm{dollar} 1.0 10{dollar}sp{lcub}-3{rcub}{dollar} pc{dollar}sp{lcub}-3{rcub}{dollar}, in accord with the results previously reported by Liebert, Dahn & Monet (1987). This space density corresponds to a white dwarf birthrate of 4.65 {dollar}times{dollar} 10{dollar}sp{lcub}-13{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar} pc{dollar}sp{lcub}-3{rcub}{dollar}. This research also details a unique approach to calculating and correcting for the incompleteness of a proper motion and magnitude selected stellar sample.