Research on the Contraction and Fragmentation of Magnetized Interstellar Clouds.

取得了如下结果：1.磁场的耗散过程可以分为两类，即等离子体漂移（双极扩散）和欧姆耗散。当主导的正、负电荷粒子被磁场冻结时，前者比后者更有效，反之，后者更有效.磁场的耗散率取决于各种带电粒子的丰度。我们研究了气相中重元素贫化的某些极限情况下的丰度，发现在密度n <10^（11）> <cm^（-3）>时，磁场的耗散时间超过自由落体时间的10倍。我们研究了两个关于云配置的典型案例。一个具有平行于其表面的磁场的盘状云，即使在磁场消散后，由于气体压力的作用，也能保持流体静力平衡。因此，这样的云即使在低密度下也会大量损失磁通量。然而，由于这样的云是引力不稳定的，并且在比通量损失时间短得多的时间尺度内分裂成碎片，因此这种云中的现象不能被认为是现实的。当磁通量小于某个临界值时，垂直磁场盘云在保持近等温的条件下，在近自由落体时间内发生收缩。因此，在n <10^（11）> <cm^（-3）> 0.4时，磁通量基本上不会损失。当n <10^（12）> <cm^（-3）>时，带正电荷和负电荷的颗粒和离子是主要的带电粒子。因为它们在如此高的密度下几乎不被冻结到磁场中，所以磁场通过欧姆加热而消散。在这种情况下，磁场几乎完全与气体解耦，并且只能存在几乎无电流的磁场。

The following results have been obtained.1. The dissipation processes of magnetic fields may be classified into two categories, the plasma drift (ambipolar diffusion) and the Ohmic dissipation. The former is more efficient than the latter when the dominant positive- and negative-charged particles are well frozen to the magnetic fields, and the latter is more efficient otherwise.2. The dissipation rate of magnetic fields depends on the abundances of various charged particles. We have investigated their abundances for some limiting cases on the depletion of heavy elements in the gas phase, and found that the dissipation time of magnetic fields exceeds 10 times the free-fall time at the density n <10^(11)> <cm^(-3)> .3. We have investigated two typical cases with regard to the cloud configuration. A disk cloud with the magnetic fields parallel to its surface can maintain hydrostatic equilibrium due to the gas pressure even after the fields have dissipated. Therefore, such a cloud can lose the magnetic flux extensively even at low densities. However, because such a cloud is gravitatioually unstable and breaks into fragments in a time scale much shorter than the flux-loss time, the phenomena in such a cloud cannot be regarded realistic. When the magnetic flux is smaller than some critical value, the disk cloud with perpendicular magnetic fields contracts in nearly the free-fall time as long as it remains nearly isothermal. Therefore, substantial loss of magnetic flux does not occur at n <10^(11)> <cm^(-3)> .4. At n <10^(12)> <cm^(-3)> the grains with positine and negative charges and the ions are the dominant charged particles. Because they are hardly frozen to the magnetic fields at such high densities, the fields dissipate by the Ohmic heating. At such a situation the magnetic fields are nearly completely decoupled from the gas, and only nearly current-free magnetic fields can exist.