The Spectral Evolution of Convective Mixing White Dwarfs, the non-DA Gap, and White Dwarf Cosmochronology

Abstract

The spectral distribution of field white dwarfs shows a feature called the "non-DA gap". As defined by Bergeron et al., this is a temperature range (5100K--6100K) where relatively few non-DA stars are found, even though such stars are abundant on either side of the gap. It is usually viewed as an indication that a significant fraction of white dwarfs switch their atmospheric compositions back and forth between hydrogen-rich and helium-rich as they cool. In this paper, we present a Monte Carlo model of the Galactic disk white dwarf population, based on the spectral evolution model of Chen and Hansen. We find that the non-DA gap emerges naturally, even though our model only allows white dwarf atmospheres to evolve monotonically from hydrogen-rich to helium-rich through convective mixing. We conclude by discussing the effects of convective mixing on the white dwarf luminosity function and the use thereof for Cosmochronology.

Submitted to ApJL on Feb. 20, 2012. Accepted on May 15, 2012

References in corpus (4)

• The White Dwarf Cooling Sequence of NGC6397
• The Ratio of Helium- to Hydrogen-Atmosphere White Dwarfs: Direct Evidence for Convective Mixing
• The Initial-Final Mass Relation among White Dwarfs in Wide Binaries
• Gravitational settling of 22Ne and white dwarf evolution

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• $Gaia$ white dwarfs within 40 pc II: the volume-limited northern hemisphere sample
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• From Hydrogen to Helium: The Spectral Evolution of White Dwarfs as Evidence for Convective Mixing
• Gaia Reveals Evidence for Merged White Dwarfs
• The spectral evolution of white dwarfs: where do we stand?
• Evidence of Spectral Evolution on the white dwarf sample from the Gaia Mission
• On the nature of the black-body stars
• Broadening of Ly alpha by neutral helium in DBA white dwarfs
• Searching for optical companions to four binary millisecond pulsars with the Gran Telescopio Canarias