Accurate Atomic Transition Probabilities for Optical Lines of Fe-group Ions

早期的宇宙几乎完全由氢和氦组成。恒星通过一系列被称为“核合成”的过程，形成行星所需的更重的化学元素，最终形成生命。最早的恒星可能与今天的恒星大不相同。这些古老的恒星被称为“贫金属”恒星，因为它们的重元素丰度很低，它们是由最早恒星的残留物形成的。金属贫乏恒星的元素丰度是我们银河系的“化石记录”，可以帮助我们了解核合成的起源。测试早期宇宙的理论需要非常精确地测量金属贫乏恒星的元素丰度。一个给定元素的精确丰度测定首先需要在我们的实验室中对该元素的原子跃迁特性进行精确的测量。该项目的目标是改进现有的元素原子数据，并利用这些数据来确定金属贫乏恒星中高度精确的丰度。这项工作也可能带来对其他应用科学领域有益的改进，比如照明和分析化学。对研究生和本科生的培训和指导一直是，并将继续是这个项目的重要组成部分。威斯康星大学（UW）的项目使用包括激光、强大光谱仪、同步辐射和其他现代方法在内的技术来测量急需的原子数据。近年来，华盛顿大学研制了一种3米梯队光谱仪，用于测量铁基团在紫外线中的极弱谱线。不像傅里叶变换光谱仪，通常用于这种测量，3m梯级光谱仪没有一个重要的（多路）噪声源。这些弱谱线在恒星光球的丰度研究中是必需的，因为较强的富铁族元素谱线部分是深度饱和的，因此不是很好的丰度指标。提出的研究将把3米梯队光谱仪的范围扩展到光学领域，用于地面天文学。该项目的第一阶段将包括开发和实施仪器的辐射校准，以达到Si探测器的极限，接近10000埃。然后，该仪器将用于测量天体物理学感兴趣的Fe、Co和Ni离子光谱中的弱光学线。这些新的跃迁概率将被应用于确定太阳和金属贫乏恒星中精确的丰度。

The early Universe was almost completely made up of hydrogen and helium. Stars build up the heavier chemical elements needed for planets and eventually for life through a series of processes known as "nucleosynthesis". The earliest stars were likely quite different than stars today. These old stars, called "metal-poor" stars because of their low abundance of heavier elements, were formed from the remnants of the earliest stars. Elemental abundances in metal-poor stars serve as a "fossil record" of our Galaxy and can help us understand the beginnings of nucleosynthesis. Testing theories of the early Universe requires very accurate measurements of elemental abundances in metal-poor stars. An accurate and precise abundance determination for a given element requires, first and foremost, accurate measurements in our laboratories of the atomic transition properties for that element. The goal of this project is to improve the available atomic data for elements and to use these data to determine highly accurate abundances in metal-poor stars. This work could also lead to improvements that benefit other fields of applied science, such as lighting and analytical chemistry. Training and mentoring of graduate students and of undergraduates has been, and will continue to be, an important part of this program. The University of Wisconsin (UW) program uses techniques involving lasers, powerful spectrometers, synchrotron radiation, and other modern approaches to measure critically needed atomic data. In recent years, a 3-meter echelle spectrometer was developed at UW to measure very weak lines of Fe-group species in the ultraviolet. Unlike Fourier transform spectrometers, which are often used for such measurements, the 3m echelle spectrometer is free from an important (multiplex) noise source. These weak lines are needed for abundance studies in stellar photospheres, because stronger lines of the abundant Fe-group elements are partially to deeply saturated and are therefore not good abundance indicators. The proposed research will extend the range of the 3m echelle spectrometer into the optical for applications in ground-based astronomy. The first phase of the project will involve developing and implementing a radiometric calibration for the instrument out to the Si detector limit near 10000 Angstroms. The instrument will then be used for the measurement of weak optical lines of astrophysical interest in the spectra of ions of Fe, Co, and Ni. These new transition probabilities will be applied to determine accurate and precise abundances in the Sun and in metal-poor stars.