Mecanism of Outflow form Dynamically Contracting Molecular Cores

研究了星际分子云的动力学收缩。1. Tomisaka用嵌套网格轴对称磁流体力学模拟研究了分子外流的机理。分子云核心的旋转放大了环面磁场，使气体以分子外流的形式喷射出去。通过模拟，我们发现：(1)初始旋转速度指定了分子流出开始的时间。即增加角动量，在绝热核形成后立即发射出流。(2)当初始极向磁场较强（其能量与热磁场相当）时，形成U型流出，其中气体主要从距离旋转轴有限距离的一个形状为大写字母U的区域流出。(3)另一种是湍流流出，其中磁力线和速度场似乎是随机定向的，这是在初始磁能远小于热能的情况下实现的。在这种情况下，气体从整体上几乎垂直地从圆盘流出，流出物看起来像一个大写字母i。考虑到磁扩散，Nakamura研究了由强磁场支持的云的引力坍缩。(1)大质量模型在早期会导致大量高密度岩心破碎。这对应于星团形成模式。(2)相反，在质量较小的云中，条状物会生长，条状物会破碎成碎片。在这种情况下，将出现一个二进制系统。

Dynamical contraction of interstellar molecular clouds is studied. 1. Tomisaka studied the mechanism of molecular outflow with the nested-grid axi-symmetric magnetohydrodynamical simulations. Rotations of the molecular cloud cores amplify the toroidal magnetic fields, which eject the gas as molecular outflows. From the simulations, we explored the followings : (1) Initial rotation speed specifies the epoch when the molecular outflow begins. That is, increasing the angular momentum, the outflow is launched immediate after the adiabatic core is formed. (2) When the initial poloidal magnetic field is strong (its energy is comparable to the thermal one), a U-shaped outflow is formed, in which gas is mainly outflowing through a region whose shape looks like a capital letter U at a finite distance from the rotation axis. (3) The other is a turbulent outflow in which magnetic field lines and velocity fields seem to be randomly oriented, which is realized when the initial magnetic energy is much smaller than the thermal one. In this case, globally the gas moves out almost perpendicularly from the disk and the outflow looks like a capital letter I. 2. Nakamura studied the gravitational collapse of a cloud supported by strong magnetic fields taking into account of the magnetic diffusion. (1) A model with large mass leads to fragmentation to a number of high-densitycores in the early phase. This corresponds to a cluster forming mode. (2) Incontrast, in a less massive cloud a bar grows and the bar breaks into fragments. In this case a binary system will appear.