RUI: Emission Line Studies of High-Velocity Interstellar Clouds using the WHAM Spectrometer

簇状高速云（HVCs）是银河系星际介质的重要组成部分，覆盖了天空的很大一部分，含有相当大的质量和动能。从定义上讲，hvc是特殊的；它们的速度不能用星系的微分旋转来解释。尽管经过了超过35年的研究，它们的起源和性质仍然是个谜。对hvc提出的解释范围很广。其中一幅画描绘了银河喷泉。在这个模型中，银河系盘面上强大的超新星爆炸将热物质喷射到平面上方的区域。然后气体冷却，凝结成云，然后像雨一样落在圆盘上。另一个著名的模型声称，hvc分散在本星系群中，这是本星系群形成时的残余。看起来，一些高速物质是被麦哲伦星云潮汐撕裂的，现在在麦哲伦星云环绕银河系的轨道上流动。最近的证据表明，一个主要的高速物质复合体的金属丰度很低，是从晕的高处吸积到盘上的。这一点特别有趣，因为长期以来，星系化学演化模型一直需要这种恒星形成所需的新鲜燃料。目前对这些模型进行区分的观测工作将加强对银河系形成及其随后的化学演化的理解，并阐明长期争论的关于银河系盘状过程与光晕之间联系的问题。之前对hvc的绝大多数研究都是使用射电望远镜来研究21厘米线，因此只探测了云中存在的中性氢。刘易斯和克拉克学院的斯蒂芬·塔夫特博士将利用威斯康星h - α绘图仪（WHAM）天文台测量光学发射线，研究与hvc相关的电离物质。WHAM是一种基于Fabry-Perot的光谱仪器，位于亚利桑那州的Kitt山顶，完全可以远程操作。观察将通过互联网在刘易斯克拉克学院校园的首席研究员实验室进行。该项目将测量来自不同hvc的氢、氮、硫和氧的发射线强度。这些观测将提供关于hvc的位置和金属丰度的信息，将对致密hvc的性质产生新的见解，并将揭示云中存在的物理条件，如它们的温度和电离状态。首席研究员已经证明了WHAM是这些研究中独特而强大的工具。新的测量方法能够区分已经提出的用于解释hvc的巨大不同的模型，因此大大提高了我们对其起源和性质的理解。该奖项是在美国国家科学基金会本科院校研究项目（RUI）的支持下颁发的

AST 0206349TufteHigh-Velocity Clouds (HVCs) are an important component of the Milky Way's interstellar medium, covering a significant fraction of the sky and containing considerable mass and kinetic energy. HVCs are by definition peculiar; they are the material with velocities not explainable by the differential rotation of the galaxy. Despite over thirty-five years of study, their origin and nature remain a mystery. Proposed explanations of HVCs span a broad range. One picture envisions a galactic fountain. In this model, powerful supernova explosions in the disk of the galaxy vent hot material into regions high above the plane. The gas then cools, condenses into clouds, and then rains back down upon the disk. Another prominent model purports that the HVCs are dispersed throughout the Local Group of galaxies, the remnants of its creation. It appears that some of the high-velocity material was tidally torn from the Magallenic clouds, and now streams behind them in their orbit around our galaxy. Recent evidence suggests that one major complex of high-velocity material has low metallicity and is accreting onto the disk from high in the halo. This is especially interesting because such fresh fuel for star formation has long been required by models of the chemical evolution of the Galaxy. Current observational efforts to distinguish between these models will enhance present understandings of the formation of the Milky Way galaxy and its subsequent chemical evolution, as well as illuminate long debated issues concerning the connection of processes in the disk of our Galaxy to the halo. The vast majority of previous investigations of HVCs have used radio telescopes to study the 21- cm line, and thus only probe the neutral hydrogen present in the clouds. Dr. Stephen Tufte, at Lewis and Clark College, will investigate ionized material associated with HVCs by making measurements of optical emission lines using the Wisconsin H-Alpha Mapper (WHAM) Observatory. WHAM is a Fabry-Perot based spectroscopic instrument that sits atop Kitt Peak in Arizona and is completely remote-operable. The observations will take place from the principal investigator's laboratory on the campus of Lewis & Clark College, by way of the Internet. This project will measure the intensities of emission lines of hydrogen, nitrogen, sulfur, and oxygen from various HVCs. The observations will provide information on the locations and metal abundances of HVCs, will yield new insights into the nature of compact HVCs, and will reveal the physical conditions present in the clouds such as their temperature and ionization state. The principal investigator has already proven WHAM to be a uniquely powerful instrument for these studies. The new measurements have the ability to distinguish between the vastly different models that have been proposed to explain HVCs, and therefore significantly advance our understanding of their origin and nature. This award is made under the auspices of the Research in Undergraduate Institutions (RUI) program at NSF.***