FINGERING CONVECTION INDUCED BY ATOMIC DIFFUSION IN STARS: 3D NUMERICAL COMPUTATIONS AND APPLICATIONS TO STELLAR MODELS
FINGERING CONVECTION INDUCED BY ATOMIC DIFFUSION IN STARS: 3D NUMERICAL COMPUTATIONS AND APPLICATIONS TO STELLAR MODELS
复制标题
恒星中原子扩散引起的指对对流：3D 数值计算及其在恒星模型中的应用
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
S. Vauclair
中科院分区：
文献类型：
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作者：
Varvara E. Zemskova;P. Garaud;M. Deal;S. Vauclair
已知富铁层是通过重力沉降和辐射悬浮的结合在恒星表面下形成的。它们的存在、性质和详细结构会影响各种恒星脉动模式的激发过程，因此必须仔细建模，以便更好地解释开普勒星震数据。本文研究了A型星中原子扩散和指状对流的相互作用及其在铁积累层建立和演化中的作用。要做到这一点，我们使用的指状对流（忽略辐射传输和复杂的不透明度的影响）和一维现实的恒星模型的三维理想化的数值模拟相结合。使用三维模拟，我们首先验证了混合处方指状对流最近提出的布朗等人。（在上述近似的范围内），并确定什么系统参数（铁的总质量，铁的扩散率，热扩散率等）。在地层的整体演化中发挥作用。然后，我们实施布朗等人。处方在图卢兹-日内瓦演化代码研究恒星表面下的铁丰度剖面的演变。我们发现，正如Théado等人首先讨论的那样，当忽略氦的同时沉降时，这种积累迅速引起平均分子量分布的反转，然后驱动指状对流。后者将铁与周围的材料非常有效地混合，并且产生的铁层非常脆弱。然而，考虑到氦沉降，部分稳定了铁的轮廓，对指状对流，和一个大的铁过剩可以积累。结果，不透明度也会显著增加，在某些情况下，它最终会触发动力对流。辐射加速对指状对流动力学的直接影响（特别是在非线性区域）仍有待于在未来加入，以提高模型的定量预测。
Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature, and detailed structure can affect the excitation process of various stellar pulsation modes and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, as well as its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection (which neglect radiative transfer and complex opacity effects) and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (within the scope of the aforementioned approximation) and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. prescription in the Toulouse-Geneva Evolution Code to study the evolution of the iron abundance profile beneath the stellar surface. We find, as first discussed by Théado et al., that when the concurrent settling of helium is ignored, this accumulation rapidly causes an inversion in the mean molecular weight profile, which then drives fingering convection. The latter mixes iron with the surrounding material very efficiently, and the resulting iron layer is very weak. However, taking helium settling into account partially stabilizes the iron profile against fingering convection, and a large iron overabundance can accumulate. The opacity also increases significantly as a result, and in some cases it ultimately triggers dynamical convection. The direct effects of radiative acceleration on the dynamics of fingering convection (especially in the nonlinear regime) remain to be added in the future to improve the quantitative predictions of the model.