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Author Gianninas, A. ♦ Bergeron, P. ♦ Dupuis, J. ♦ Ruiz, M. T.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ ABUNDANCE ♦ BALMER LINES ♦ CARBON ♦ FAR ULTRAVIOLET RADIATION ♦ GRAVITATION ♦ HELIUM ♦ HYDROGEN ♦ LTE ♦ METALS ♦ NITROGEN ♦ OXYGEN ♦ STAR EVOLUTION ♦ STELLAR ATMOSPHERES ♦ STELLAR WINDS ♦ WHITE DWARF STARS ♦ ATMOSPHERES ♦ DWARF STARS ♦ ELECTROMAGNETIC RADIATION ♦ ELEMENTS ♦ EQUILIBRIUM ♦ EVOLUTION ♦ FLUIDS ♦ GASES ♦ NONMETALS ♦ RADIATIONS ♦ RARE GASES ♦ STARS ♦ STELLAR ACTIVITY ♦ ULTRAVIOLET RADIATION
Abstract We present an analysis of optical spectra for 29 DAO white dwarfs. First, we present our new up-to-date model atmosphere grids computed without the assumption of local thermodynamic equilibrium in which we have included carbon, nitrogen, and oxygen at solar abundances. We demonstrate that the addition of these metals in the model atmospheres is essential in overcoming the Balmer-line problem, which manifests itself as an inability to fit all the Balmer lines simultaneously with consistent atmospheric parameters. We then present the spectroscopic analysis of our sample of DAO white dwarfs for which we determine the effective temperature, surface gravity, and helium abundance. We also present 18 hot DA white dwarfs that also suffer from the Balmer-line problem. We analyze these stars with models analogous to those for the DAO white dwarfs save for the presence of helium. Systematic differences between our newly determined atmospheric parameters with respect to previous determinations are explored. Far-ultraviolet spectra from the FUSE archive are then examined to demonstrate that there exists a correlation between higher metallic abundances and instances of the Balmer-line problem. The implications of these findings for all hot, hydrogen-rich white dwarfs are discussed. Specifically, the possible evolutionary scenario for DAO white dwarfs is revised and post-extreme horizontal branch evolution is no longer needed to explain the evolution for the majority of the DAO stars. Finally, we discuss how the presence of metals might drive a weak stellar wind which in turn could explain the presence of helium in DAO white dwarfs.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2010-09-01
Publisher Place United States
Journal Astrophysical Journal
Volume Number 720
Issue Number 1


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