The instability of fast shocks in molecular clouds
The instability of fast shocks in molecular clouds
复制标题
分子云中快速激波的不稳定性
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
A. Rosen
中科院分区：
文献类型：
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作者：
Michael D. Smith;A. Rosen
我们报告的发现，中等快速冲击致密的分子云与低横向磁场可能是不稳定的。这种不稳定性是由一氧化碳和水分子在延伸的暖激波段中形成的促进冷却所触发的。数值方法表明，在没有磁场的情况下，不稳定的制度是限制在NO = 10 - 4 cm - 3以上的密度，速度在30-70 km s - 1之间，和O或C丰度以上10 - 4，使冷却重整分子占主导地位的温暖的气体，而不受抑制的紫外线离解。其结果是一个准周期或混乱的崩溃和重建的暖激波层上的一个典型的时间尺度为10 6 cm - 3 /n 0 yr的变化较短的时间尺度和周期的变化是可能的。来自不稳定区域的红外发射线，包括H2线，表现出数量级的变化.原子线，如哈显示恒定的通量，但经历快速的径向速度变化。
We report on the discovery that moderately fast shocks in dense molecular clouds with low transverse magnetic fields are likely to be unstable. The instability is triggered by the promoted cooling that results from the formation of carbon monoxide and water molecules in an extended warm shock section. Numerical methods are employed to demonstrate that, in the absence of magnetic fields, the instability regime is restricted to densities above no = 10 4 cm - 3 , velocities between 30-70 km s - 1 , and O or C abundances above ∼10 - 4 , so that cooling from reforming molecules dominates in the warm gas without being suppressed by ultraviolet dissociation. The result is either a quasi-periodic or chaotic collapse and re-establishment of the warm shock layer on a typical time-scale of 10 6 cm - 3 /n 0 yr with variations on shorter time-scales and changes in period being possible. Infrared emission lines from the unstable region, including the H 2 lines, exhibit orders of magnitude variability. Atomic lines such as Ha display constant fluxes but undergo rapid radial velocity variations.