A COMPREHENSIVE SPECTROSCOPIC ANALYSIS OF DB WHITE DWARFS

Journal Article · Wed Aug 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/737/1/28· OSTI ID:21579987

Bergeron, P; Wesemael, F; Dufour, Pierre; Beauchamp, A; Hunter, C; Gianninas, A; Limoges, M -M; Dufour, Patrick; Fontaine, G ^[1]; Saffer, Rex A ^[2]; Ruiz, M T ^[3]; Liebert, James ^[4]

---

1. Departement de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-Ville, Montreal, QC H3C 3J7 (Canada)
2. Strayer University, 234 Mall Boulevard, Suite G-50, King of Prussia, PA 19406 (United States)
3. Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile)
4. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

We present a detailed analysis of 108 helium-line (DB) white dwarfs based on model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a mean mass of 0.67 M{sub sun} for our sample, with a dispersion of only 0.09 M{sub sun}. White dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample, and their mass distribution appears similar to that of DB stars. As in our previous investigation, we find no evidence for the existence of low-mass (M < 0.5 M{sub sun}) DB white dwarfs. We derive a luminosity function based on a subset of DB white dwarfs identified in the Palomar-Green Survey. We show that 20% of all white dwarfs in the temperature range of interest are DB stars, although the fraction drops to half this value above T{sub eff} {approx} 20,000 K. We also show that the persistence of DB stars with no hydrogen features at low temperatures is difficult to reconcile with a scenario involving accretion from the interstellar medium, often invoked to account for the observed hydrogen abundances in DBA stars. We present evidence for the existence of two different evolutionary channels that produce DB white dwarfs: the standard model where DA stars are transformed into DB stars through the convective dilution of a thin hydrogen layer and a second channel where DB stars retain a helium atmosphere throughout their evolution. We finally demonstrate that the instability strip of pulsating V777 Her white dwarfs contains no non-variables, if the hydrogen content of these stars is properly accounted for.

• OSTI ID: 21579987
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 737; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
DISTRIBUTION
DWARF STARS
ELEMENT ABUNDANCE
ELEMENTS
EVOLUTION
FIELD THEORIES
FLUIDS
FUNCTIONS
GASES
GRAND UNIFIED THEORY
HELIUM
HYDROGEN
LUMINOSITY
MASS DISTRIBUTION
MATHEMATICAL MODELS
NONMETALS
OPTICAL PROPERTIES
PARTICLE MODELS
PHYSICAL PROPERTIES
QUANTUM FIELD THEORY
RARE GASES
SPATIAL DISTRIBUTION
STANDARD MODEL
STAR EVOLUTION
STARS
UNIFIED GAUGE MODELS
WHITE DWARF STARS