Radio Scattering in Galactic and Extra-Galactic Astronomy

由巴尼·里克特博士领导的这个项目的目标是：(1)确定一些非常紧凑的射电源的角结构；(2)测量星际等离子体中的小尺度湍流；(3)研究波在湍流介质中的传播。这些目标是非常不同的科学领域，与将在工作中使用的无线电散射方法相关。当类星体和脉冲星的无线电信号向地球传播时，它们会受到类似于地球大气中闪烁的星光的散射，只是原因是星际等离子体密度的波动。虽然这种散射阻碍了对类星体或脉冲星的直接研究，但它提供了一个星际等离子体的探测器和一种测量源中非常微小的结构的方法。在最简单的形式下，它是基于恒星闪烁而行星不闪烁的常见观测--因为行星的角大小比恒星大，这就消除了闪烁。由于不同的原因，将用这些技术研究的来源特别有趣。一个是最近发现的双脉冲星双星系统J0737-3039。该系统是研究引力物理和脉冲星磁球的卓越实验室。里克特博士的研究将有助于实现引力和磁层研究的潜力。另一类来源是所谓的“日内变量”。这些是活动星系核，它们是如此致密，以至于它们一定非常明亮，事实上，它们如此明亮，以至于它们非常接近“逆康普顿极限”。里克特博士的研究将有助于确定是否真的违反了逆康普顿极限。一些散射技术已经成熟，只需要改进，而另一些技术，如最近在脉冲星光谱中发现的“抛物线弧线”，前景广阔，但仍处于初级阶段。这些技术的发展是这项工作的重要组成部分。这包括开发数字模拟工具来研究分析上难以解决的案例。星际等离子体的微观结构还不是很清楚，测量大多局限于一维，但新的技术已经开始提供二维图像，这将被大力推进。这项工作影响了天文学的几个领域：脉冲星、引力、银河系外来源和星际介质。技术的发展，特别是数字模拟，也将在天文学之外产生广泛的影响，包括太阳风等离子体，以及波在大气和海洋中的传播。该奖项主要用于支持研究生和本科生。他们将接受的培训在科学和工程的许多分支中具有广泛的适用性。

AST 0507713RickettThe objectives of this project, led by Dr. Barney Rickett, are: (1) to determine the angular structure of some very compact radio sources; (2) to measure the small-scale turbulence in the interstellar plasma; and (3) to study the propagation of waves through turbulent media. These objectivesare quite disparate areas of science, related by the radio scattering methods that will be employed in the work. As the radio signals from quasars and pulsars travel toward the Earth, they suffer scattering analogous to the twinkling of starlight in the Earth's atmosphere, except that the cause is fluctuations in the density of the interstellar plasma. Though this scattering hampers the direct study of the quasar or pulsar, it provides a probe of the interstellar plasma and a method of measuring very small structure in the source. In its simplest form it is based on the familiar observation that stars twinkle and planets don't - because planets have a larger angular size than stars and this smoothes out the twinkling. The sources that will be studied with these techniques are particularly interesting for different reasons. One is the recently discovered double pulsar binary system J0737-3039. This system is a remarkable laboratory for studies of gravitational physics and pulsar magneto-spheres. Dr. Rickett's studies will help realize the potential for gravitational and magnetospheric studies. Another class of source is the so-called "intra-day variable." These are active galactic nuclei which are so compact that they must be incredibly bright, in fact so brightthat they come very close to the "inverse Compton limit." Dr. Rickett's studies will help determine if indeed the inverse Compton limit is violated. Some of the scattering techniques are mature and need only refinement, whereas others, such as the "parabolic arcs" recently discovered in pulsar spectra, have great promise but are still in their infancy. The development of these techniques is an important part of this work. This includes the development of digital simulation tools to study cases which are analytically intractable. The microstructure of the interstellar plasma is not well understood and measurements have been for the most part restricted to one dimension, but new techniques have already started to provide a two dimensional view and this will be pursued vigorously.The work impacts several areas of astronomy: pulsars; gravitation; extra-galactic sources; and interstellar medium. The development of techniques, particularly digital simulations, will also have a broad impact outside astronomy, including the solar wind plasma, and wave propagation in the atmosphere and in the ocean. This award is primarily for the support of graduate and undergraduate students. The training they will receive has broad applicability in many branches of science and engineering.