论文标题
分子离子的碰撞极化：双极扩散的路标
Collisional polarization of molecular ions: a signpost of ambipolar diffusion
论文作者
论文摘要
磁场在许多天体物理过程的动力学中起作用，但很难检测到它们。在部分离子化的等离子体中，磁场直接在电离培养基上起作用，而在中性培养基上不起作用，这会导致它们之间的速度漂移：双极扩散。该过程被认为在恒星形成过程中很重要，但从未直接观察到。我们引入了一种可用于检测双极扩散的方法和引起它的磁场，在该方法中我们利用了带电和中性培养基之间的速度漂移。通过使用碰撞动力学的代表性经典模型，我们表明当分子离子与其主要碰撞伴侣H2之间存在速度漂移时，分子离子会部分对齐。我们证明，双相扩散会比其临界密度更密集地比对分子离子，这随后导致这些物种的部分极化发射。我们包括一个用于HCO+的模型，并表明可以检测到通过内部原始磁盘区域的数值模拟预测的双相漂移。极化向量垂直于投射在天空平面上的磁场方向。
Magnetic fields play a role in the dynamics of many astrophysical processes, but they are hard to detect. In a partially ionized plasma, a magnetic field works directly on the ionized medium but not on the neutral medium, which gives rise to a velocity drift between them: ambipolar diffusion. This process is suggested to be important in the process of star formation, but has never been directly observed. We introduce a method that could be used to detect ambipolar diffusion and the magnetic field that gives rise to it, where we exploit the velocity drift between the charged and neutral medium. By using a representative classical model of the collision dynamics, we show that molecular ions partially align themselves when a velocity drift is present between the molecular ion and its main collision partner H2. We demonstrate that ambipolar diffusion potently aligns molecular ions in regions denser than their critical density, which subsequently leads to partially polarized emission from these species. We include a model for HCO+ and show that collisional polarization could be detectable for the ambipolar drifts predicted by numerical simulations of the inner protostellar disk regions. The polarization vectors are aligned perpendicular to the magnetic field direction projected on the plane of the sky.
