大质量恒星中的对流及其对恒星结构演化的影响

发布时间：2018-01-04 18:17

本文关键词：大质量恒星中的对流及其对恒星结构演化的影响　出处：《中国科学院研究生院（云南天文台）》2014年博士论文　论文类型：学位论文

【摘要】：大质量恒星内部对流特征与中小质量恒星有很大不同。在中小质量星的主序阶段，恒星是由对流核、辐射平衡壳层以及处于它们中间的辐射平衡中间层组成，这个中间层的化学元素分布不均匀。然而在大质量恒星主序阶段，这个化学元素分布不均匀区域会出现“半对流”现象。在本文中，我们采用史瓦西（Schwarzchild）方法和勒都（Ledoux）方法这两种不同的方法来分别处理15M⊙和30M⊙恒星的“半对流”和对流超射。这两种方法的不同之处在于对流边界以及熵梯度所采用的公式不同：当采用史瓦西方法时，熵梯度sc r=pHp(ad)；当采用勒都方法时，熵梯度s r=cpHp(adμ)。中心核对流超射与中间区域中的“半对流”被当成一个整体进行处理。通过计算，我们发现，中心核对流超射与“半对流”所呈现的发展趋势几乎相反，，当中心核对流超射增强的时候，“半对流”将减弱，反之亦然。本文通过模型计算，分析了不同参数以及不同对流处理方法对中心核超射区以及“半对流”区的湍流特征的影响。增大湍流模型中混合长参数α导致中心对流核的湍动能增加，并且使中心对流超射距离增加，但是会抑制“半对流”的发展。采用勒都方法来处理湍对流将使超射距离增加并抑制“半对流”的出现和发展。同时，本文用扩散过程模拟近似对流超射及“半对流”对元素分布的影响。本文引用一个扩散参数D来控制对流超射以及“半对流”对元素分布的影响程度。这不同于别的研究者们采用不同参数来分别处理对流超射以及“半对流”区的元素扩散过程。湍流元素扩散混合对化学元素分布演化以及H-R图的影响在本文中也得以体现。
[Abstract]:The convection characteristics of large mass stars are very different from those of medium and small mass stars. In the main sequence stage of medium and small mass stars, the stars are composed of convective nuclei, radiation equilibrium shells and radiation equilibrium intermediate layers in the middle of them. The distribution of chemical elements in this interlayer is not uniform. However, in the main sequence of massive stars, "semi-convection" occurs in this region. We use the Schwarzchilds method and Ledoux). Methods these two different methods are used to deal with the "semi-convection" and convection overshoot of 15m-and 30m-298 stars, respectively. The difference between these two methods is that the convection boundary and the entropy gradient are different. When using the Schwartz method. Entropy gradient sc rn. When the Ledu method is used, the entropy gradient s r n c pH p + + 渭 n. The central nucleus flow overshoot and the "semi-convection" in the middle region are treated as a whole. By calculation, we find that the central nucleus flow overshoot and the "semi-convection" in the middle region are treated as a whole. The development trend of the central nucleus stream overshoot and "semi-convection" is almost opposite. When the central nucleus stream overshoot increases, the "semi-convection" will weaken, and vice versa. The model calculation is carried out in this paper. The effects of different parameters and different convection processing methods on the turbulent characteristics of the central nucleus overshoot region and the "semi-convection" region are analyzed. Increasing the mixing long parameter 伪 in the turbulence model results in the increase of the turbulent kinetic energy of the central convection nucleus. Moreover, the overshoot distance of central convection is increased, but the development of "semi-convection" is restrained. Using the Ledu method to deal with the turbulent convection will increase the overshoot distance and restrain the appearance and development of "semi-convection". In this paper, the effect of approximate convection overshoot and "semi-convection" on element distribution is simulated by diffusion process. A diffusion parameter D is used to control convection overshoot and "semi-convection". The degree of influence on the distribution of elements. This is different from other researchers using different parameters to deal with convective overshoot and "semi-convection", respectively. The effects of turbulent element diffusion and mixing on the chemical element distribution evolution and H-R diagram are also reflected in this paper.
【学位授予单位】：中国科学院研究生院（云南天文台）
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P152

【参考文献】