Hot White Dwarfs in the Extreme Ultraviolet Explorer Survey. II. Mass Distribution, Space Density, and Population Age

Details Hot White Dwarfs in the Extreme Ultraviolet Explorer Survey. II. Mass Distribution, Space Density, and Population Age Hot White Dwarfs in the Extreme Ultraviolet Explorer Survey. II. Mass Distribution, Space Density, and Population Age

May 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...480..714v&link_type=abstract

Astrophysical Journal v.480, p.714

Statistics

107

Stars: White Dwarfs, Stars: Fundamental Parameters, Stars: Evolution, Stars: Statistics, Ultraviolet: Stars

Scientific paper

We present new effective temperature and surface gravity determinations for a sample of 90 hot white dwarfs detected in the Extreme Ultraviolet Explorer (EUVE) all-sky survey. The measurements, based on spectroscopy of the Balmer line series obtained at the Michigan-Dartmouth-MIT Observatory, Mount Stromlo Observatory, Lick Observatory, and Cerro Tololo Inter-American Observatory, are used to constrain the space density as well as the population age and mass distribution of a sample of 110 EUV-selected DA white dwarfs in the solar neighborhood. We find a mass spectrum narrowly peaked over 0.56 M&sun;, indicative of a C-O core with a thin hydrogen layer, and a significant population of 10 ultramassive (M >= 1.1 M&sun;) white dwarfs; we also find that all objects fall between effective temperatures of ~25,000 and ~75,000 K and that most are younger than 30 Myr. Using Wood's evolutionary models we determine a DA white dwarf birthrate in the solar neighborhood of (0.7--1.0) x 10-12 pc-3 yr-1. Although most objects are on normal C-O cooling tracks, we suggest that a few low-mass white dwarfs and the population of ultramassive white dwarfs may follow different paths with, respectively, He, and, possibly, O-Ne-Mg cores.

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