描述恒星内部对流超射的经典方法是非局地混合长理论，但是，这种理论是唯象理论，建立在不牢固的基础上。最近，日震学研究否定了非局地混合长理论框架下的对流超射图景，同时表明，目前只有使用湍流模型描述对流超射才能产生符合日震学的结果。这为研究恒星内部的对流超射指明了方向。 本论文首先对湍流模型进行理论分析，得到了湍流模型的近似解和超射区中的渐近解，了解了超射区的结构。然后，将湍流模型包含在恒星结构演化程序中，计算了太阳模型，发现湍流模型描述下的对流超射区的温度梯度轮廓与日震学反演结果很好的符合，使用合适的超射混合强度可以同时大幅改善太阳模型的 Li 丰度、声速轮廓和密度轮廓。本论文还利用星团中的 Li 丰度研究了扩散型对流超射混合的影响。在双星 HY Vir 模型的研究中，本文利用该双星系统的观测性质研究了扩散型对流超射混合的合适强度，然后研究了使用湍流模型和扩散型对流超射混合的情况下的恒星内部结构特点。最后，本文建立了湍流化学组分通量的湍流模型，解出了对流和超射混合的扩散系数，得到了超射混合的新模型，利用恒星的一些观测特性计算了模型参数的取值，还研究了对流超射区中流体的运动特点。
其他摘要
The classical method on the convective overshoot is the non-local mixing length theories. These theories are phenomenological method which are not based on fluid dynamics. Recently, helioseismic investigations have showed that the profile of temperature gradient of the solar overshoot region is out of non-local mixing length theories, suggested that only turbulent convection models can lead to consistence, and pointed out the direct of studying convective overshoot. In this thesis, the the turbulent convection model has been studied, and its approximate solution and the asymptotical solution in overshoot region have been obtained. The solar evolutionary models have been studied. It is found that the temperature gradient profile, which results from the turbulent convection model, near the base of the solar convection zone is consistent with the helioseismic inversion. The solar sound speed, density, and lithium abundance at the solar surface can be significantly improved when the diffusive overshoot mixing with a proper intensity is taken into account. The diffusive overshoot mixing is adopted in studying lithium abundance in open cluster. In the binary star HY Vir, the observations have been used to calibrate the intensity of diffusive overshoot mixing, and the properties of stellar models of HY Vir based on the turbulent convection model and diffusive overshoot mixing have been investigated. It has been found that all the observations show that the best value of the parameter in the simple diffusive overshoot mixing model is too low, which indicates the simple diffusive overshoot mixing model is not physically reasonable. In order to study the overshoot mixing, a turbulent model of convective/overshoot mixing has been establish, the diffusion coefficient of convective/overshoot mixing has been worked out. It has been found that the diffusion coefficient show distinct property in convection zone and overshoot region. The proper value in the new turbulent model of convective/overshoot mixing has been obtained by comparing theoretical stellar models with observations.
修改评论