存在风车扭矩时的辐射扭矩校准
Radiative torques alignment in the presence of pinwheel torques
摘要：
我们研究的晶粒排列受到辐射扭矩和风车扭矩，同时占粮食的热翻转。我们所说的风车力矩是指所有固定在颗粒体轴线上的系统力矩，包括由各向同性辐射的散射和吸收引起的辐射力矩。讨论了由红外辐射引起的系统转矩和热等离子体中粒子与离子、电子相互作用引起的系统转矩。我们表明，这两种类型的扭矩是长寿命的，即可能存在的时间比气体阻尼时间。我们将这些力矩与E. Purcell，即H $_2$形成的力矩、气体碰撞的调节系数变化和光电发射。此外，我们修正了Lazarian和Draine模型的晶粒热翻转。我们计算平均翻转时间尺度引起的Barnett和核弛豫的顺磁性和超顺磁性颗粒，在存在的随机扭矩与风车扭矩，例如随机扭矩所产生的H $_2$形成，和气体轰击。我们表明，内部松弛和随机扭矩的综合作用可以导致足够小的晶粒快速翻转，正因为如此，他们得到热陷阱，即热旋转，尽管存在的风车扭矩。对于足够大的晶粒，我们表明，风车扭矩可以增加的程度实现与辐射扭矩的晶粒对齐，通过增加低吸引子点的角动量的大小和/或通过驱动晶粒到新的高吸引子点。
英文摘要：
We study the alignment of grains subject to both radiative torques and pinwheel torques while accounting for thermal flipping of grains. By pinwheel torques we refer to all systematic torques that are fixed in grain body axes, including the radiative torques arising from scattering and absorption of isotropic radiation. We discuss new types of pinwheel torques, which are systematic torques arising from infrared emission and torques arising from the interaction of grains with ions and electrons in hot plasma. We show that both types of torques are long-lived, i.e. may exist longer than gaseous damping time. We compare these torques with the torques introduced by E. Purcell, namely, torques due to H$_2$ formation, the variation of accommodation coefficient for gaseous collisions and photoelectric emission. Furthermore, we revise the Lazarian & Draine model for grain thermal flipping. We calculate mean flipping timescale induced by Barnett and nuclear relaxation for both paramagnetic and superparamagnetic grains, in the presence of stochastic torques associated with pinwheel torques, e.g. the stochastic torques arising from H$_2$ formation, and gas bombardment. We show that the combined effect of internal relaxation and stochastic torques can result in fast flipping for sufficiently small grains and, because of this, they get thermally trapped, i.e. rotate thermally in spite of the presence of pinwheel torques. For sufficiently large grains, we show that the pinwheel torques can increase the degree of grain alignment achievable with the radiative torques by increasing the magnitude of the angular momentum of low attractor points and/or by driving grains to new high attractor points.
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