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首页> 外文期刊>Space Science Reviews >Obtaining Spectra of Turbulent Velocity from Observations
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Obtaining Spectra of Turbulent Velocity from Observations

机译：通过观测获得湍流速度谱

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We discuss a long-standing problem of how turbulence can be studied using observations of Doppler broadened emission and absorption lines. The focus of the present review is on two new techniques, the Velocity–Channel Analysis (VCA), which makes use of the channel maps, and the Velocity Coordinate Spectrum (VCS), which utilizes the fluctuations measured along the velocity axis of the Position–Position Velocity (PPV) data cubes. Both techniques have solid theoretical foundations based on analytical calculations as well as on numerical testings. Among the two the VCS, which has been developed quite recently, has two unique features. First of all, it is applicable to turbulent volumes that are not spatially resolved. Second, it can be used with absorption lines that do not provide good spatial sampling of different lags over the image of the turbulent object. In fact, recent studies show that measurements of absorption line along less than 10 absorption directions are sufficient for a reliable recovering of the underlying spectrum of the turbulence. Moreover, both weak absorption lines and absorption lines in saturated regime can be used, which extends the applicability of the technique. Our comparison of the VCA and the VCS with a more traditional technique of Velocity Centroids shows that the former two techniques recover reliably the spectra of supersonic turbulence, while the Velocity Centroids may be used only for studying subsonic turbulence. We discuss spectra of astrophysical turbulence obtained with the VCA and the VCS techniques. Keywords Turbulence - MHD - Interstellar medium PACS 95.30.Qd - 52.30.Cv - 96.50.Tf - 98.38.Gt
机译：我们讨论了一个长期存在的问题，即如何使用多普勒变宽的发射和吸收谱线来研究湍流。本文的重点是两种新技术：利用通道图的速度通道分析（VCA）和利用沿位置速度轴测得的波动的速度坐标谱（VCS） –位置速度（PPV）数据多维数据集。两种技术都具有基于分析计算和数值测试的坚实理论基础。在这两个VCS中，最近开发的VCS具有两个独特的功能。首先，它适用于没有空间解析的湍流体积。其次，它可以与吸收线一起使用，这些吸收线不能在湍流物体的图像上提供不同滞后的良好空间采样。实际上，最近的研究表明，沿着小于10个吸收方向的吸收线测量值足以可靠地恢复湍流的潜在光谱。此外，可以使用弱吸收线和饱和状态下的吸收线，这扩展了该技术的适用性。我们对VCA和VCS与较传统的速度质心技术的比较表明，前两种技术能够可靠地恢复超音速湍流的频谱，而速度质心仅可用于研究亚音速湍流。我们讨论了用VCA和VCS技术获得的天体湍流谱。湍流-MHD-星际介质PACS 95.30.Qd-52.30.Cv-96.50.Tf-98.38.Gt

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