CALIBRATION OF THE MIXING-LENGTH THEORY FOR CONVECTIVE WHITE DWARF ENVELOPES
CALIBRATION OF THE MIXING-LENGTH THEORY FOR CONVECTIVE WHITE DWARF ENVELOPES
复制标题
对流白矮星包层混合长度理论的校准
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
P. Brassard
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文献类型：
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作者：
P. Tremblay;H. Ludwig;B. Freytag;B. Freytag;G. Fontaine;M. Steffen;P. Brassard
本文给出了纯氢大气白色矮星对流区下部局域混合长度理论（MLT）中混合长度参数的一种标定。的参数化进行比较的三维（3D）CO 5 BOLD模拟与网格的一维（1D）信封具有不同的混合长度参数。在许多情况下，3D模拟仅限于对流区的上部。流体动力学计算表明，在这些情况下，从对流区底部到光球层正下方的区域，上升流的熵没有显著变化。我们依赖于这个渐近熵值，深和分层的层的特性，校准1D信封。校准包括对流氢线（DA）白色在有效温度范围6000 <$Teff（K）<$15，000和表面重力范围7.0 <$log g <$9.0。它是建立在本地MLT是无法同时再现的3D模拟的结晶，通量和动力学特性。因此，我们提出了三种不同的参数化这些数量。由此产生的校准可以应用于结构和包络计算，特别是脉动，化学扩散和对流混合的研究。另一方面，对流对白色矮星的冷却速率没有影响，直到有一个与简并核心的对流耦合低于Teff 5000 K。在这种情况下，1D结构是不敏感的MLT参数化，并收敛到平均3D结果，因此，他们仍然完全适合年龄测定。
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 ⩽ Teff (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 Teff ∼ 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.