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Calibration of the mixing-length theory for convective white dwarf envelopes
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Tremblay, Pier-Emmanuel, Ludwig, H.-G., Freytag, B., Fontaine, G., Steffen, M. and Brassard, P. (2015) Calibration of the mixing-length theory for convective white dwarf envelopes. The Astrophysical Journal, 799 (2). 142. doi:10.1088/0004-637X/799/2/142 ISSN 0004-637X.
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Official URL: http://dx.doi.org/10.1088/0004-637X/799/2/142
Abstract
A calibration of the mixing-length parameter in the local mixing-length theory (MLT) is presented for the lower part of the convection zone in pure-hydrogen-atmosphere white dwarfs. The parameterization is performed from a comparison of three-dimensional (3D) CO5BOLD simulations with a grid of one-dimensional (1D) envelopes with a varying mixing-length parameter. In many instances, the 3D simulations are restricted to the upper part of the convection zone. The hydrodynamical calculations suggest, in those cases, that the entropy of the upflows does not change significantly from the bottom of the convection zone to regions immediately below the photosphere. We rely on this asymptotic entropy value, characteristic of the deep and adiabatically stratified layers, to calibrate 1D envelopes. The calibration encompasses the convective hydrogen-line (DA) white dwarfs in the effective temperature range 6000 ≤ T eff (K) ≤15, 000 and the surface gravity range 7.0 ≤ log g ≤ 9.0. It is established that the local MLT is unable to reproduce simultaneously the thermodynamical, flux, and dynamical properties of the 3D simulations. We therefore propose three different parameterizations for these quantities. The resulting calibration can be applied to structure and envelope calculations, in particular for pulsation, chemical diffusion, and convective mixing studies. On the other hand, convection has no effect on the white dwarf cooling rates until there is a convective coupling with the degenerate core below T eff ~ 5000 K. In this regime, the 1D structures are insensitive to the MLT parameterization and converge to the mean 3D results, hence they remain fully appropriate for age determinations.
Item Type: | Journal Article | ||||||||
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Subjects: | Q Science > QB Astronomy | ||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||
Library of Congress Subject Headings (LCSH): | Convection (Astrophysics), Hydrodynamics, Stars -- Evolution, White dwarf stars | ||||||||
Journal or Publication Title: | The Astrophysical Journal | ||||||||
Publisher: | Institute of Physics Publishing, Inc. | ||||||||
ISSN: | 0004-637X | ||||||||
Official Date: | 23 January 2015 | ||||||||
Dates: |
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Volume: | 799 | ||||||||
Number: | 2 | ||||||||
Article Number: | 142 | ||||||||
DOI: | 10.1088/0004-637X/799/2/142 | ||||||||
Status: | Peer Reviewed | ||||||||
Publication Status: | Published | ||||||||
Access rights to Published version: | Restricted or Subscription Access | ||||||||
Date of first compliant deposit: | 27 October 2016 | ||||||||
Date of first compliant Open Access: | 27 October 2016 | ||||||||
Funder: | Hubble Space Telescope (Spacecraft) (HST), United States. National Aeronautics and Space Administration (NASA), Sonderforschungsbereich 881 -- "The Milky Way System", Deutsche Forschungsgemeinschaft (DFG) | ||||||||
Grant number: | HF-51329.01 (HST), NAS 5-26555 (NASA) | ||||||||
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