Chemical Composition Studies of Galactic Halo and Disk Populations

斯内登博士和他的团队研究了银河系盘状和晕状恒星的化学成分，这为我们银河系的诞生和演化提供了线索。这项工作结合了中高分辨率的光谱观测、仔细的丰度分析和改进的实验室原子物理数据，以确定光晕、盘场和星系星的大样本的准确丰度数据，从而深入了解我们银河系的化学演化。对大样本的分析将提供更多统计上可靠的样本，以了解银河系中重元素含量从几乎为零到目前富金属的太阳化学成分到底发生了什么。银河系化学演化的研究是通过四个不同但相互关联的任务完成的。首先，研究了一个新的大样本非常贫金属的晕群场恒星的中子俘获元素丰度。这极大地扩展了分析的恒星样本，同时将丰度集限制在可以在极低金属丰度恒星的光谱中检测到的四种关键元素。其次，对数百到数千颗单个球状星系星的金属度和元素丰度比进行了测量，以获得从星系团主序列到其红色巨型分支尖端的极大演化和光度范围内的光谱。在一种方法中，将采用几个球状星系团中数十万颗恒星的有限波长覆盖的多目标光谱，以检查是否可以从一个星系团的所有恒星中获得一致的金属度和铁族元素丰度比。任何与光度有关的变化都可能使标准化学成分分析中的基本假设受到质疑。在另一种方法中，利用更多球状星团中大光度范围内恒星的大波长覆盖的多目标光谱来检验这些自包含恒星系统中轻挥发性元素的产生理论。第三，对银河系疏散星团演化恒星的金属度、CNO丰度和碳同位素(12C/13C)比值进行了新的调查。这种方法首次结合了可见光和红外光谱区域的光谱特征覆盖范围，以便准确地获得单个星系团的红巨星枝上下恒星中氢燃烧产物的丰度。第四，对太阳和贫金属星的铁族元素跃迁进行了持续的实验室和恒星研究，以提高基本恒星丰度分析的准确性。计算机代码和原子线数据的不断开发和免费传播给世界各地的恒星光谱学家社区。重点是对计算机代码进行重大更改，以自动进行化学成分分析。作为该项目的一部分，正在进行的一个涉及中学教育工作者团体的计划将得到扩大，新的重点是为教育工作者提供远程观测机会。

Dr. Sneden and his team study the chemical compositions of stars in the Milky Way's disk and halo, which hold clues to the birth and evolution of our Galaxy. This work combines medium to high resolution spectroscopic observations, careful abundance analyses, and improved laboratory atomic physics data to determine accurate abundance data for large samples of halo and disk field and cluster stars that provide insights on the chemical evolution of our Galaxy.The analysis of large samples will provide more statistically robust samples to understand what really has happened to build the Milky Way's heavy element content from virtually zero to the present metal-rich solar chemical composition. The study of Galactic chemical evolution is done through four different but connected tasks here.First, a new large-sample of neutron-capture elemental abundances in very metal-poor halo population field stars is studied. This greatly expands the analyzed stellar sample, while limiting the abundance set to four key elements that can be detected in the spectra of very low metallicity stars. This is used to track the range of element production that can occur in rapid-blast neutron-capture nucleosynthetic environments.Second, the metallicity and elemental abundance ratios of hundreds to thousands individual globular cluster stars are surveyed to obtain spectra over an extremely large evolution and luminosity range, from the cluster main sequences to the tips of their red giant branches. In one approach, multi-object spectra with limited wavelength coverage of hundreds-thousands of stars in a few globular clusters will be taken to check whether consistent metallicities and abundance ratios of iron-group elements can be obtained from all stars of a cluster. Any luminosity dependent variations could call into question the underlying assumptions in standard chemical composition analyses. In another approach, multi-object spectra of large wavelength coverage of stars over large luminosity ranges in many more globular clusters are used to test the theories of production of the light volatile elements in these self-contained stellar systems.Third, a new survey of metallicities, CNO abundances, and carbon isotope (12C/13C) ratios is undertaken for evolved stars of Galactic open clusters. The approach here combines for the first time coverage of spectral features in both the visible and infrared spectral regions , in order to obtain accurate abundances of H-burning products in stars up and down the red giant branches of individual clusters. These in turn provide more complete descriptions of evolution and mixing in metal-rich disk stellar systems.Fourth, continued laboratory and stellar studies of iron-group element transitions in the Sun and in metal-poor stars are conducted to bring heightened accuracy to basic stellar abundance analyses.There is continued development and free dissemination of computer codes and atomic line data to the world-wide community of stellar spectroscopists. Emphasis is placed on significant changes to the computer codes to perform chemical composition analyses automatically. As part of this project, an ongoing program involving a secondary-school educator group will be expanded, with new emphasis on remote observing opportunities for the educators.