Atomic Hydrogen As A Probe Of Molecular Cloud Structure And Evolution

Paul金匠博士将利用这个奖项来研究HI窄线自吸收（HINSA）的分子云结构的新探针。虽然我们对新恒星形成的密集寒冷区域的理解已经取得了许多进展，但仍然存在许多重要的问题。这些包括：（1）分子云的结构，包括决定其温度和电离状态的加热和冷却过程;（2）分子云的寿命，特别是与星星形成的时间尺度有关的寿命;（3）磁场的作用。对21厘米谱线的观测将产生重要的信息，补充从分子和尘埃的高频观测中获得的信息。这一研究项目将通过提供关于分子云寿命的重要信息，提供关于致密区域关键过程的重要信息，包括关于颗粒表面H2形成和宇宙射线加热率的重要信息，加强我们对分子云和新星如何形成的了解;特别是从原子到分子的转换开始到新恒星形成之间的时间延迟，通过开发一种新的技术来测量密集区域中的磁场，具有更高的灵敏度，并通过提供在合理的时间内产生视线磁场强度图的能力。分子氢是密集区域中最丰富的分子，星际介质中屏蔽良好的区域，但极难直接追踪。现在看来，通过仔细测量与致密分子云核心相关的原子氢，我们可以了解更多关于从原子到分子形式的转变，从而了解致密区域的演化，从接近原子到最终大部分分子。HI/H2比值可以作为星际云演化的计时器，测量它们向星星形成阶段的演化。磁场及其与物质的相互作用对星际介质中发生的许多过程至关重要，包括星星和行星的形成。这种重要性激励了许多研究人员，但关于核心演化和坍缩的磁场强度的初始条件的信息很少。目前的工作将证明磁场的塞曼测定方法是如此有效，以至于将首次绘制出稠密云中磁场（视线）值的大小图，这是有道理的。这些数据将是一个强有力的动机，继续理论研究的一系列磁流体动力学（MHD）的主题，包括研究MHD湍流及其衰减在稠密的云和磁场的关系，磁盘，射流和分子外流。新的结果将解决与天文学中许多重要问题密切相关的问题，包括初始质量函数和星系的化学演化。星星形成的话题显然是广泛的兴趣群体的老年人，大学退休人员，和学生在纯粹的本科院校都看到分子云和星星形成的话题，他们可以联系。预计在这项研究计划的过程中，金匠博士。将继续为这些团体举办讲座。通过将分子云中的化学问题与原始太阳系中的化学问题联系起来，并将我们正在研究的磁场与太阳系形成的原恒星盘中的磁场联系起来，这项工作将对广泛的受众产生影响。***

Dr. Paul Goldsmith will use this award to pursue a novel probe of molecular cloud structure for the study of HI narrow line self absorption, or HINSA. While there have been many advances in our understanding of the dense, cold regions where new stars form, there remain many important questions. These include (1) the structure of molecular clouds including heating and cooling processes which determine their temperature and ionization state; (2) the lifetime of molecular clouds, in particular related to the time scale for star formation; and (3) the role of the magnetic field. The observations of the 21cm line will yield vital information, complementary to that obtained from higher frequency observations of molecules and dust. This research project will enhance our understanding of molecular clouds and how new stars are formed by providing important information on key processes in dense regions, including the grain surface H2 formation and the cosmic ray heating rate, by giving important information on the lifetime of molecular clouds; in particular the time delay between the onset of atomic to molecular conversion and the formation of new stars, by developing a new technique for measuring the magnetic field in dense regions, with much enhanced sensitivity, and by offering the capability of producing maps of line of sight magnetic field strength in a reasonable time.Molecular hydrogen is the most abundant molecule in dense, well shielded regions of the interstellar medium, but is extremely difficult to trace directly. It now appears possible, that by careful measurements of the atomic hydrogen associated with dense molecular cloud cores, we can learn much about the transition from atomic to molecular form and thus of the evolution of dense regions, starting from being nearly atomic and ending up as largely molecular. The HI/H2 ratio can serve as a chronometer for the evolution of interstellar clouds and measure their evolution towards the phase in which they are the sites of star formation. The magnetic field and its interaction with matter are critical for a number of processes that occur in the interstellar medium, including star and planet formation. This importance has motivated many researchers,but there is very little information about the initial conditions in terms of magnetic field strength, for core evolution and collapse. It is plausible that the present work will prove so effective a method of Zeeman determination of the magnetic field, that there will for the first time be maps of the magnitude of the (line of sight) value of the magnetic field in dense clouds. These data will be a strong motivation for continued theoretical studies on a range of magnetohydrodynamic (MHD) topics, including studies of MHD turbulence and its decay in dense clouds and the relationship of the magnetic field to disks, jets, and molecular outflows. The new results will address questions closely tied to many important issues in astronomy including the initial mass function and the chemical evolution of galaxies. The topic of star formation is clearly of wide interest Groups of senior citizens, university retirees, and students at purely undergraduate institutions all see molecular clouds and star formation as topics to which they can relate. It is anticipated that in the course of this research program, Dr. Goldsmith. will continue to give talks to these groups. By connecting the issue of the chemistry in molecular clouds to that in the primitive solar system, and by linking the magnetic field we are studying to that in protostellar disks such as that from which our solar system formed, this work will have an impact on a broad audience. ***