我们能在星前核中观测到离子中性漂移速度吗？
Can we observe the ion-neutral drift velocity in prestellar cores?
摘要：
由于分子云的电离率很低，双极扩散被认为是恒星形成的一个完整过程。然而，化学和辐射转移效应，观测的挑战，以及事实上，离子中性漂移速度本质上是非常小的呈现一个明确的双极扩散的检测非常不平凡。在这里，我们研究了离子中性漂移速度在一套化学动力学，非理想磁流体动力学（MHD），二维轴对称模拟的星前核，我们改变温度，宇宙射线电离率，视觉消光，质量流量比，和化学演变。随后，我们进行了一些非本地热力学平衡（非LTE）辐射传输计算，考虑各种理想化和非理想化的情况下，以评估哪个因素（化学，辐射转移和/或观测困难）是最具挑战性的，以克服我们的努力，以检测离子中性漂移速度。我们发现，温度具有显着的影响，在最冷的模拟核心（T = 6 K）表现出漂移速度的幅度的漂移速度与声速。与预期相反，我们发现，在理想化的情况下（两个物种是完美的化学共同进化）的漂移速度"生存”的辐射转移效应，并在原则上可以观察到。然而，我们发现，观测的挑战和化学效应可以显着阻碍我们的观点的离子中性漂移速度。最后，我们建议，$\rm{HCN}$和$\rm{HCNH^+}$，是化学共同发展，可用于未来的观测研究，旨在测量离子中性漂移速度。
英文摘要：
Given the low ionization fraction of molecular clouds, ambipolar diffusion is thought to be an integral process in star formation. However, chemical and radiative-transfer effects, observational challenges, and the fact that the ion-neutral drift velocity is inherently very small render a definite detection of ambipolar diffusion extremely non-trivial. Here, we study the ion-neutral drift velocity in a suite of chemodynamical, non-ideal magnetohydrodynamic (MHD), two-dimensional axisymmetric simulations of prestellar cores where we alter the temperature, cosmic-ray ionization rate, visual extinction, mass-to-flux ratio, and chemical evolution. Subsequently, we perform a number of non-local thermodynamic equilibrium (non-LTE) radiative-transfer calculations considering various idealized and non-idealized scenarios in order to assess which factor (chemistry, radiative transfer and/or observational difficulties) is the most challenging to overcome in our efforts to detect the ion-neutral drift velocity. We find that temperature has a significant effect in the amplitude of the drift velocity with the coldest modelled cores (T = 6 K) exhibiting drift velocities comparable to the sound speed. Against expectations, we find that in idealized scenarios (where two species are perfectly chemically co-evolving) the drift velocity ``survives" radiative-transfer effects and can in principle be observed. However, we find that observational challenges and chemical effects can significantly hinder our view of the ion-neutral drift velocity. Finally, we propose that $\rm{HCN}$ and $\rm{HCNH^+}$, being chemically co-evolving, could be used in future observational studies aiming to measure the ion-neutral drift velocity.
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