TP-AGB星超星风物理机制

发布时间：2018-05-25 05:48

本文选题：恒星演化 + 热脉冲AGB星　；参考：《浙江师范大学》2011年硕士论文

【摘要】：在恒星演化过程中湍流压常被忽略,但其对流区固有的大尺度湍流使得湍流压必然存在。本文通过对3～10M⊙恒星在赫罗图上演化轨迹的研究,并分析恒星内部氦壳层燃烧峰值处能量、密度、温度、氦壳层表面光度与恒星表面光度比及恒星半径的变化,给出了中等质量恒星由早期AGB星演化至热脉冲AGB星阶段在赫罗图上的分界点,与119颗碳星的观测结果吻合得相当好。同时提出：在恒星演化至该分界点之后,其星风物质损失公式可能需要引入一个与表面光度无关的量以主导超星风的形成。在此基础上,通过对考虑湍流压效应下5Mo恒星的结构和演化及星风物质损失率的分析,发现湍流压在热脉冲AGB星阶段对星风物质损失影响较大,从而使得热脉冲AGB星的湍流压不可忽略。在虑及湍流压对星风物质损失的可能影响之后,我们对恒星的外壳进行了详细的分析,以期了解湍流在超星风形成机制中所扮演的可能角色。通过对恒星演化过程中恒星外壳对流区马赫数极大值处各种压强、对流元马赫数、引力加速度、及该处以外质量大小的分析,发现恒星外壳对流区出现的可压缩流体对恒星质量损失存在一定的影响,从而尝试在考虑星风物质损失机制时引入可压缩流体机制,提出新的星风物质损失公式。应用新的星风物质损失公式对3～5M⊙恒星质量损失率进行计算,并将其与经典星风物质损失公式的计算结果对比。发现从主序直至中心氦核燃烧结束阶段,新的星风物质损失公式计算所得星风物质损失率与经典星风物质损失公式计算结果几近一致,在后期则不受光度影响产生了持续的较大的星风物质损失率,比较符合实际观测结果。
[Abstract]:In the process of star evolution, turbulence pressure is often ignored, but the large scale turbulence inherent in the convection region makes the turbulence pressure inevitable. In this paper, we study the evolution track of 310M ~ (-) star on Hero diagram, and analyze the changes of energy, density, temperature, surface luminosity of helium shell and star radius at the peak value of helium shell burning in the interior of the star, and the relation between the surface luminosity of the helium shell and the surface luminosity of the star. The boundary points of the medium mass stars from the early AGB stars to the thermal pulse AGB stars on the Hero diagram are given, which are in good agreement with the observations of 119 carbon stars. At the same time, it is suggested that after the star evolves to the boundary point, it may be necessary to introduce a quantity independent of surface luminosity to dominate the formation of superstar wind. On the basis of the analysis of the structure and evolution of 5Mo stars and the loss rate of stellar wind matter considering the turbulent pressure effect, it is found that the turbulent pressure has a great influence on the loss of stellar wind matter in the thermal pulse AGB star stage. Thus the turbulent pressure of the thermal pulse AGB star can not be ignored. After taking into account the possible influence of turbulence pressure on the loss of stellar wind material, we have made a detailed analysis of the shell of a star in order to understand the possible role of turbulence in the formation mechanism of superstar wind. Based on the analysis of various pressures, Mach numbers of convection elements, gravitational acceleration, and mass outside the convective region of a star during the evolution of a star, the maximum value of Mach number in the convection region of a star is analyzed. It is found that the compressible fluid in the convective region of the stellar shell has a certain influence on the mass loss of the star. Therefore, the compressible fluid mechanism is introduced into account of the mechanism of the stellar wind mass loss, and a new formula for the loss of the stellar wind mass is proposed. The mass loss rate of the star is calculated by using the new formula of stellar wind mass loss, and the results are compared with those of the classical formula of stellar wind mass loss. It is found that from the main sequence to the end of the central helium core combustion, the calculated results of the new formula for calculating the loss rate of the star wind matter are almost consistent with the results of the classical formula for the star wind mass loss. In the later stage, the star wind material loss rate is large and consistent with the observed results.
【学位授予单位】：浙江师范大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：P144

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