Chemical Composition Studies of Galactic Halo and Disk Populations

银河晕和盘族的化学成分研究

• 批准号: 1211585
• 负责人: Christopher Sneden
• 金额: $ 24.61万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1211585&HistoricalAwards=false
• 关键词: Chemical; Composition; Studies; Galactic; Halo

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.

Sneden博士和他的团队研究了银河系盘和晕中恒星的化学成分，这些成分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，以及改进实验室原子物理数据，以确定晕和盘场和星团恒星的大样本的准确丰度数据，这些数据提供了对银河系化学演化的见解。对大样本的分析将提供更具统计学意义的样本，以了解银河系重元素含量的真实情况从几乎为零到现在富含金属的太阳化学成分。银河系化学演化的研究是通过四个不同但相互联系的任务来完成的：首先，研究了一个新的大样本的中子捕获元素丰度非常贫金属晕人口场恒星。这极大地扩展了分析的恒星样本，同时将丰度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。这是用来跟踪的范围内的元素生产，可以发生在快速爆炸中子捕获nucleosynthetic environments.Second，金属丰度和元素丰度比的数百至数千个单独的球状星团恒星进行了调查，以获得光谱在一个非常大的演变和光度范围内，从集群的主要序列的红巨星分支的尖端。在一种方法中，将采用几个球状星团中数十万颗恒星的有限波长覆盖的多目标光谱，以检查是否可以从星团的所有恒星中获得一致的金属丰度和铁族元素丰度比。任何光度相关的变化都可能对标准化学成分分析中的基本假设提出质疑。在另一种方法中，多目标光谱的大波长覆盖的恒星在大的光度范围内，在更多的球状星团被用来测试的轻挥发性元素的生产理论，在这些独立的恒星system.Third，一个新的调查的金属丰度，CNO丰度，和碳同位素（12 C/13 C）的比例进行了银河系疏散星团的演化恒星。这里的方法结合了第一次在可见光和红外光谱区域的光谱特征的覆盖范围，以获得准确的丰度的H-燃烧产品的恒星向上和向下的红巨星分支的个别集群。第四，继续进行太阳和贫金属恒星中铁族元素跃迁的实验室和恒星研究，以提高基本恒星丰度分析的准确性，继续发展计算机代码和原子线数据，并免费分发给全世界的恒星光谱学家。重点放在计算机代码的重大变化，以自动进行化学成分分析。 作为该项目的一部分，将扩大一个涉及中学教育工作者团体的持续方案，并将新的重点放在教育工作者的远程观察机会上。