Laboratory Spectroscopy for Studies of Metal-Poor Halo Stars

用于贫金属晕恒星研究的实验室光谱学

• 批准号: 0205124
• 负责人: James Lawler
• 金额: $ 20.75万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0205124&HistoricalAwards=false
• 关键词: Laboratory; Spectroscopy; Studies; Metal; Poor

AST 0205124LawlerThe study of abundances of the heavy elements in metal-poor halo stars is contributing to a more quantitative understanding of stellar nucleosynthesis and Galactic chronometry. The odd-even sawtooth pattern of abundances throughout the lanthanides is examined to separate out thecontributions of the r- and s- processes (synthesis by rapid and slow neutron capture) throughoutthe evolution of the Galaxy. The abundances of the radioactive chronometers Th and U aremeasured along with abundances of other near-lying r-process elements such as Os, Ir and Pt todetermine stellar age and thereby put a lower limit on the Galactic age. Abundance accuracy is key in these studies, and yet the database of transition probabilities on which the abundance determination depends is sorely lacking for many of the heavy elements. Often astronomers must make use of solar gf-values which have many sources of uncertainty, particularly for heavy elements which are relatively weak in comparison to the Fe group in the solar spectrum. Old laboratory measurements and semi-empirical results are also often used, although they are known to have large errors for weaker lines. With modern beam-laser techniques, gf-values can be eliminated as the major source of uncertainty in solar and stellar abundance determinations.Dr. James Lawler and colleagues, at the University of Wisconsin, will conduct laboratory measurements of large sets of accurate, absolute transition probabilities. Transition probabilities will be determined by combining radiative lifetimes with branching fractions. The radiative lifetimes will be measured using time-resolved laser-induced fluorescence on a slow beam of atoms/ions. Branching fractions will be measured using Fourier transform spectroradiometry. Priority will be given to the lanthanide spectrum Nd II, as well as spectra of important chronometers Th II and U II. The gf-values of these spectra have been identified as the most in need of improvement, and as critical in studies of halo stars. As time and resources allow, measurements will continue on the spectra Os I, Pt I and Ir I, which have also been identified as needing improved gf-values, and as important in studies of halo stars.****

对缺乏金属的晕星中重元素丰度的研究有助于更定量地了解恒星核合成和银河系计时学。整个镧系元素丰度的奇偶锯齿模式被检查，以分离出整个星系演化过程中r-和s-过程（通过快中子和慢中子捕获合成）的贡献。放射性计时器Th和U的丰度与其他邻近r过程元素（如Os、Ir和Pt）的丰度一起测量，以确定恒星的年龄，从而为银河系的年龄设定一个下限。丰度准确性是这些研究的关键，但许多重元素的丰度测定所依赖的跃迁概率数据库严重缺乏。通常，天文学家必须利用太阳的gf值，因为它有许多不确定的来源，特别是与太阳光谱中的Fe族相比相对较弱的重元素。旧的实验室测量和半经验的结果也经常被使用，尽管他们已知有较大的误差较弱的线。使用现代光束激光技术，可以消除作为太阳和恒星丰度测定不确定性的主要来源的gf值。威斯康辛大学的James Lawler和他的同事将在实验室对大量精确的绝对跃迁概率进行测量。跃迁概率将通过结合辐射寿命和分支分数来确定。辐射寿命将测量使用时间分辨激光诱导荧光慢束原子/离子。分支分数将使用傅里叶变换光谱测量法进行测量。将优先考虑镧系元素的光谱Nd II，以及重要的计时器Th II和U II的光谱。这些光谱的gf值已被确定为最需要改进的，并且在晕星的研究中至关重要。在时间和资源允许的情况下，将继续对Os I， Pt I和Ir I光谱进行测量，这些光谱也被认为需要改进gf值，并且在晕星的研究中同样重要。****