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arXiv 1503.04582astro-ph.SR
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基于3D对流模拟校准的混合长度和T（tau）关系的恒星模型

Stellar models with mixing length and T(tau) relations calibrated on 3D convection simulations

Maurizio Salaris, Santi Cassisi

备注：
6 pages, 3 figures, accepted for publication in A&A
发表信息：
A&A 577, A60 (2015)
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摘要：

对流包层恒星模型中超绝热层的热分层计算是恒星天体物理学中一个长期存在的问题，对恒星半径和有效温度等观测性质的预测有重要影响。混合长度理论，几乎普遍用于模拟超绝热对流层，有效地包含一个自由参数进行校准-α（毫升）-其值控制产生的有效温度。在这里，我们提出了第一个自洽的恒星演化模型，通过使用大气温度分层，Rosseland不透明度和校准变量alpha（ml）（取决于有效温度和表面重力）从一个大型的三维辐射流体动力学模拟恒星对流信封和大气太阳恒星组成（Trampedach等人，2013）。从我们的计算（具有相同的辐射流体动力学模拟组成），我们发现，与恒定太阳α（ml）计算的模型相比，具有流体校准变量α（ml）的模型的有效温度仅显示微小的差异，最多约30-50 K。在这两种情况下，对流区的深度基本相同。我们还分析了水文校准的T（tau）关系在确定模型有效温度的演变中所起的作用，当与恒星模型计算中经常使用的替代T（tau）关系相比时。与恒定的太阳值相比，T（tau）的选择可以具有比使用变量alpha（ml）更大的影响。我们发现Vernazza等人（1981）的太阳半经验T（tau）提供的恒星模型有效温度与水校正关系的结果相当一致。

英文摘要：

(abridged) The calculation of the thermal stratification in the superadiabatic layers of stellar models with convective envelopes is a long standing problem of stellar astrophysics, and has a major impact on predicted observational properties like radius and effective temperature. The Mixing Length Theory, almost universally used to model the superadiabatic convective layers, contains effectively one free parameter to be calibrated --alpha(ml)-- whose value controls the resulting effective temperature. Here we present the first self-consistent stellar evolution models calculated by employing the atmospheric temperature stratification, Rosseland opacities, and calibrated variable alpha(ml) (dependent on effective temperature and surface gravity) from a large suite of three-dimensional radiation hydrodynamics simulations of stellar convective envelopes and atmospheres for solar stellar composition (Trampedach et al. 2013). From our calculations (with the same composition of the radiation hydrodynamics simulations), we find that the effective temperatures of models with the hydro-calibrated variable alpha(ml) display only minor differences, by at most ~30-50 K, compared to models calculated at constant solar alpha(ml). The depth of the convective regions is essentially the same in both cases. We have also analyzed the role played by the hydro-calibrated T(tau) relationships in determining the evolution of the model effective temperatures, when compared to alternative T(tau) relationships often used in stellar model computations. The choice of the T(tau) can have a larger impact than the use of a variable alpha(ml) compared to a constant solar value. We found that the solar semi-empirical T(tau) by Vernazza et al. (1981) provides stellar model effective temperatures that agree quite well with the results with the hydro-calibrated relationships.

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