Disorientation of Suprathermally Rotating Grains and the Grain Alignment Problem
Disorientation of Suprathermally Rotating Grains and the Grain Alignment Problem
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超热旋转晶粒的迷失方向和晶粒排列问题
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
B. Draine
中科院分区：
文献类型：
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作者：
A. Lazarian;B. Draine
我们讨论了尘埃颗粒受到氢气形成产生的扭矩的动力学。特别是，我们讨论了当颗粒旋转并经历“交叉”事件时的颗粒动力学。正如 Spitzer 和 McGlynn 首先指出的那样，交叉事件之前和之后的颗粒角动量是相关的，并且这种相关的程度严重影响顺磁耗散引起的尘埃颗粒的排列。我们计算相关性，包括谷物材料内热波动的重要影响。这些波动限制了颗粒角动量J与最大惯性颗粒主轴a1耦合的程度。我们表明，a1 与 J 的这种不完美耦合在交叉过程中起着至关重要的作用，并且可以显着提高大于 0.1 μm 的晶粒的顺磁排列效率。结果，我们表明，对于参数的合理选择，如果不存在星光引起的辐射扭矩，则可以通过超热旋转颗粒中的顺磁耗散来实现所观察到的 ≳ 0.1 μm 颗粒的排列。我们还表明，在长对准时间的限制下，机械对准的效率不会因颗粒材料中的热波动而改变。
We discuss the dynamics of dust grains subjected to torques arising from H2 formation. In particular, we discuss grain dynamics when a grain spins down and goes through a “crossover” event. As first pointed out by Spitzer & McGlynn, the grain angular momentum before and after a crossover event are correlated, and the degree of this correlation critically affects the alignment of dust grains by paramagnetic dissipation. We calculate the correlation including the important effects of thermal fluctuations within the grain material. These fluctuations limit the degree to which the grain angular momentum J is coupled with the grain principal axis a1 of maximal inertia. We show that this imperfect coupling of a1 with J plays a critical role during crossovers and can substantially increase the efficiency of paramagnetic alignment for grains larger than 0.1 μm. As a result, we show that for reasonable choices of parameters, the observed alignment of a ≳ 0.1 μm grains could be achieved by paramagnetic dissipation in suprathermally rotating grains, if radiative torques caused by starlight were not present. We also show that the efficiency of mechanical alignment in the limit of long alignment times is not altered by the thermal fluctuations in the grain material.