Dust grains and the structure of steady C-type magnetohydrodynamic shock waves in molecular clouds
Dust grains and the structure of steady C-type magnetohydrodynamic shock waves in molecular clouds
复制标题
尘埃颗粒与分子云中稳定C型磁流体动力冲击波的结构
DOI：
10.1046/j.1365-8711.1998.01641.x
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发表时间：
1998
影响因子：
4.8
通讯作者：
M. Wardle
中科院分区：
文献类型：
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作者：
M. Wardle
我检查尘埃颗粒的作用，在确定结构的稳定，冷，斜C型冲击致密分子气体。忽略气体压力、带电组分的惯性和电离的变化。电子中性和颗粒中性弹性散射的颗粒电荷和速率系数被假定为常数，其值适合于激波内部。一个MRN尺寸分布占估计有效的晶粒丰度和霍尔参数为单一尺寸的晶粒。 对于每一个冲击速度vs，在中间信号速度vA cos θ和θ 2 vA cot θ之间存在一个单参数的中间冲击族，其中vA是冲击前阿尔芬速度，θ是冲击前磁场和冲击波阵面法线之间的夹角。此外，对于每个vs > vA，存在唯一的快速冲击。 如果冲击前密度nH <$105 cm−3和冲击前磁场满足B（mG）/nH（105 cm−3 <$1，则颗粒与磁场部分解耦，并且快冲击内的场和速度分量不位于包含冲击前场和冲击法线的平面内。由此产生的激波结构比不考虑这一点的模型要薄得多。现有的模型系统地低估了冲击波阵面内的颗粒中性漂移速度和加热速率。当密度超过108 cm −3时，这些效应可能会因正负粒子的丰度几乎相等而减弱。
I examine the role of dust grains in determining the structure of steady, cold, oblique C-type shocks in dense molecular gas. Gas pressure, the inertia of the charged components and changes in ionization are neglected. The grain charge and rate coefficients for electron–neutral and grain–neutral elastic scattering are assumed constant at values appropriate to the shock interior. An MRN size distribution is accounted for by estimating an effective grain abundance and Hall parameter for single-size grains. A one-parameter family of intermediate shocks exists for each shock speed vs between the intermediate signal speed vA cos θ and √2vA cot θ, where vA is the pre-shock Alfven speed and θ is the angle between the pre-shock magnetic field and the normal to the shock front. In addition, there is a unique fast shock for each vs > vA. If the pre-shock density nH ≳ 105 cm−3 and the pre-shock magnetic field satisfies B(mG)/nH(105 cm−3 ≲ 1, grains are partially decoupled from the magnetic field and the field and velocity components within fast shocks do not lie in the plane containing the pre-shock field and the shock normal. The resulting shock structure is significantly thinner than in models that do not take this into account. Existing models systematically underestimate the grain–neutral drift speed and the heating rate within the shock front. At densities in excess of 108 cm −3 these effects may be reduced by the nearly equal abundances of positive and negative grains.