Temperatures, gravities, and masses for a sample of bright DA white dwarfs and the initial-to-final mass relation

Abstract

The atmospheric parameters, T<SUB>eff</SUB> and log g, have been determined for a sample of 52 hydrogen-line (DA) white dwarfs by fitting optical spectra to theoretical model atmospheres. Multiple observations of each star allow an estimation of the accuracy of the method: the average external errors are 490 K in T<SUB>eff</SUB> and 0.06 in log g. Masses have been derived using white dwarf evolutionary models where finite temperature effects are taken into account. The average mass of the 46 DA stars in our sample with T<SUB>eff</SUB> greater than 12,000 K is 0.587 solar masses, with a dispersion of 0.166 solar masses while the mode of the distribution is between 0.50 and 0.55 solar masses. The mass distribution shows a low-mass (M less than 0.4 solar masses) tail of four objects which are most likely helium white dwarfs, the outcome of close binary evolution. Excluding those objects, the average mass becomes 0.609 solar masses, with a dispersion of 0.157 solar masses. When combining with the sample studied by Bergeron, Saffer, &amp; Liebert (1992), this leads to a set of 164 white dwarfs for which atmospheric parameters and masses have been obtained in a homogeneous way. In this sample 15 objects have M less than 0.4 solar masses, thus confirming that about 10% of catalog white dwarfs are helium white dwarfs produced in close binaries. The implications for the stellar initial mass-final mass relation are then discussed in some detail. Some individual objects of particular astrophysical interest are also briefly discussed.