论文标题
关于天体物理流体涡度的测量
On the Measurement of Vorticity in Astrophysical Fluids
论文作者
论文摘要
涡度对于湍流的性质和动态过程至关重要，包括天体物理流体的湍流。因此，Cygnus Loop Supernova Remnant的旋转液中涡流的\ cite {raymond20a，raymond20b}的结果引起了极大的兴趣。我们考虑光学上薄线的光谱测量值是最常见的天文赛车测定法，可以产生流体中涡度的明确测量。我们认为在流动平面上观察的理想情况可能包含或可能不包含涡度。在一种情况下，该流动具有垂直于观测平面的方向的涡度。在另一种情况下，通过构造流动是无关的（零涡度）。观察到的涡度（称为{\ em pseudOvorticity}）是根据速度的视线组成部分的空间差异和对称性假设来推断的。我的主要结果是，在涡旋流动的情况下，伪层性是真正涡度的合理匹配。然而，重要的是，在不旋转流场的情况下，伪病态也非零，与涡流流相比。本文的结论是，虽然天文学光谱观察结果可能会对远程流体中的涡度进行良好的估计，但这种推论的鲁棒性无法得到保险。
Vorticity is central to the nature of, and dynamical processes in turbulence, including turbulence in astrophysical fluids. The results of \cite{Raymond20a,Raymond20b} on vorticity in the post-shock fluid of the Cygnus Loop supernova remnant are therefore of great interest. We consider the degree to which spectroscopic measurements of an optically-thin line, the most common type of astronomical velocimetry, can yield unambiguous measurements of the vorticity in a fluid. We consider an ideal case of observations in the plane of a flow which may or may not contain vorticity. In one case, the flow possesses vorticity in a direction perpendicular to the plane of observations. In the other case, the flow is irrotational (zero vorticity) by construction. The observationally-deduced vorticity (referred to as the {\em pseudovorticity}) is inferred from spatial differences in the line-of-sight component of velocity, and assumptions of symmetry. My principal result is that in the case of the vortical flow, the pseudovorticity is a reasonable match for the true vorticity. However, and importantly, the pseudovorticity in the case of the irrotational flow field is also nonzero, and comparable in magnitude to that for a vortical flow. The conclusion of this paper is that while astronomical spectroscopic observations may yield a good estimate of the vorticity in a remote fluid, the robustness of such an inference cannot be insured.
