Study on Early Evolution of Protostars based on Tree-dimensional Radiative Magnetohydrodynamical Numeroca ; l Simulations

本项目的目的是在考虑自重、磁场和辐射传输的数值模拟的基础上，研究与盘和伴星有关的原星的演化。我们构建了PC集群，开发了使用AMR(自适应网格加密)的数值模拟代码，并出版了数值格式和数据分析手册，以维护我们的数值模拟研究的基础。主要科学成果如下：1.首次采用嵌套网格对旋转磁化分子云的引力坍缩进行了三维数值模拟。我们发现，在原恒星形成时期，磁力和离心力的总和收敛到某一值，而与初始磁场和自转无关。当离心力大于离心力时，云团趋于碎裂，形成二元云。2.推导了求解两相气体热演化的最小空间分辨率。空间分辨率应该小于热传递的典型标度长度的三分之一。3.我们已经证明，初级气体比伴生气体倾向于共生更多的气体。这否定了气体吸积应该增加质量比的传统观点。4.我们用三维数值模拟来跟踪原始气体的引力崩塌。模拟结果表明，在族III恒星中，双星形成的频率也应该很高。5.我们对超新星爆发进行了一维数值模拟。它们表明，超新星爆炸通过压缩周围的星际气体，在1万年内促进了第二代恒星的形成。

This project is aimed to study evolution of protostars associated with disks and companions on the basis of numerical simulation in which self-gravity, magnetic field, and radiative transfer are taken into account. We have constructed PC cluster, developed numerical simulation codes employing AMR(adaptive mesh refinement), and published manuals on numerical schemes and data analysis, in order to maintain the basis for our numerical simulation studies. Main scientific achievements are as follows.1.We have performed three-dimensional numerical simulations of gravitational collapse of rotating magnetized molecular cloud with the nested grid for the first time. We have found that the total of the magnetic and centrifugal forces converges at a certain value at the epoch of the protostar formation irrespectively of the initial magnetic field and rotation. When the centrifugal force dominates over the centrifugal force, the cloud tends to fragment to form binary.2.We have derived minimum spatial resolution to solve the thermal evolution of two phase gases. The spatial resolution should be smaller than a third of the typical scale length for the heat transfer.3.We have shown that the primary tends to accrete more gas than the companion. This denies the conventional idea that gas accretion should increase the mass ratio.4.We have followed gravitational collapse of primordial gas with three-dimensional numerical simulations. The simulations suggest that frequency of binary formation should be high also in population III stars.5.We have performed one-dimensional numerical simulations of supernova explosion. They show that the supernova explosions promote formation of the second generation stars within 10 thousands years through compression of the surrounding interstellar gas.