Improved Simulations of Cosmic Plasmas: Measurements and Modeling Studies of Thermal Energy Charge Transfer in Support of Ground-Based Astronomy

改进的宇宙等离子体模拟：支持地面天文学的热能电荷转移的测量和建模研究

• 批准号: 0307203
• 负责人: Daniel Wolf Savin
• 金额: $ 25.17万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0307203&HistoricalAwards=false
• 关键词: Improved; Simulations; Cosmic; Plasmas; Measurements

AST 0307203SavinIt has long been recognized that thermal energy charge transfer (CT) of singly- and doubly chargedions with atomic hydrogen plays an important role in determining the ionization structure, thermalstructure, emission spectrum, and absorption spectrum of planetary nebulae, H II regions, Lya clouds, the intergalactic medium (IGM), and shocks in supernova remnants and Herbig-Haro objects. Ground-based spectroscopic observations of these sources are used to address many fundamental questions in astrophysics such as the primordial He abundance, the chemical evolution of the universe, the shape of the metagalactic radiation field as a function of redshift, galactic chemical evolution, and stellar nucleosynthesis. Of particular importance to address these issues are reliable thermal energy CT rate coefficients for singly- and doubly-charged ions of C, N, and O.The majority of thermal CT data used in astrophysics has been calculated with the Landau-Zener (LZ) method. Dr. Daniel Wolf Savin's laboratory results have demonstrated that LZ calculations of thermal CT cross section can be off by up to an order of magnitude. A few state-of-the-art molecular orbital close-coupling (MOCC) calculations also exist. But laboratory work has shown that without benchmark measurements, MOCC thermal CT cross section calculations can be off by up to a factor of 3.Dr. Savin and colleagues will carry out a combined program of laboratory measurements and modeling studies for CT of C2+, N+, N2+, O+, and O2+ on atomic H at thermal energies. They have already carried out such measurements for C+. The new measurements will be carried out using the Oak Ridge National Laboratory ion-atom merged-beams apparatus which is the only existing facility capable of carrying out the proposed thermal energy cross section measurements.The results will be used to benchmark state-of-the-art MOCC calculations. The measurements, in combination with benchmarked theory if needed, will also be used to produce CT rate coefficientswith an estimated accuracy of 20%. The group will publish simple fits to derived rate coefficientsso that the astrophysics community can use the new data in their studies of cosmic plasmas.Concurrent with the measurements, they will carry out modeling studies using CLOUDY toinvestigate the astrophysical implication of the new data as well as the implication due to anyinferred uncertainties in the unmeasured CT data for other ions. Some of the issues to be investigated include the role that CT plays in determining the ionization correction factors used toinfer the primordial He abundance from H II regions. The group will also study the role of CT in Lya clouds and the IGM, observations of which are used to constrain the chemical evolution of theuniverse and the shape of the metagalactic radiation field as a function of redshift.A large portion of this research project will be carried out by a Columbia University graduatestudent in partial fulfillment of the requirements for her/his Ph.D. Teaching and training of thestudent will be overseen by Dr. Savin and collaborators at Oak Ridge National Laboratory (ORNL), the University of Kentucky, and the University of Georgia-Athens. The research will thereby result in the education and training of a student to be a future scientist. In addition this work will enhance the Columbia/ORNL infrastructure for research and education which Dr. Savin has recently established with his collaborators at ORNL. The measurements will be carried out in collaboration with ORNL scientists using a unique ORNL facility. Lastly, to enhance scientific and technical understanding the group will broadly disseminate the results at conferences and publish themin the appropriate scientific journals.***

早已认识到，AST 0307203SVINIT已确认，与原子氢的单一和双重充电的热能电荷转移（CT）在确定电离结构，热结构，发射光谱和吸收光谱中起着重要作用和Herbig-Haro对象。这些来源的基于地面的光谱观测来解决天体物理学中的许多基本问题，例如原始的HE丰度，宇宙的化学演化，元层流辐射场的形状，作为红移，银河化学化学进化和恒星核合成的函数。解决这些问题的重要性是可靠的热能CT速率系数，用于C，N和O的单个C，N和O。天体物理学中使用的大多数热CT数据是用Landau-Zener（LZ）方法计算的。 丹尼尔·沃尔夫·萨维（Daniel Wolf Savin）博士的实验室结果表明，热CT横截面的LZ计算可以通过数量级的顺序排列。还存在一些最先进的分子轨道关闭偶联（MOCC）计算。但是实验室的工作表明，如果没有基准测量，MOCC热CT横截面计算可以减少3.dr。 Savin及其同事将对在热能量下的原子H上进行C2+，N+，N2+，O+和O2+CT的实验室测量和建模研究。 他们已经对C+进行了此类测量。新的测量将使用橡树岭国家实验室离子离子合并的梁设备进行，这是唯一能够进行拟议的热能横截面测量值的现有设施。结果将用于基准最先进的MOCC计算。这些测量结果与基准理论（如果需要）结合使用，也将用于产生CT速率系数，估计精度为20％。 该小组将发布简单的拟合，以得出速率系数，即天体物理学社区可以在宇宙等离子体的研究中使用新数据。与测量结果相关，他们将使用云层进行建模研究，以弥补新数据的天体含义，以及由于无限制的不可限制的含义而导致了其他无效数据的含义。要调查的一些问题包括CT在确定使用HII区域的原始元素中的电离校正因子中所起的作用。该小组还将研究CT在Lya云和IGM中的作用，其观察被用来限制Universe的化学演化以及元层次辐射领域的形状随红移的函数。该研究项目的大部分地区将由哥伦比亚大学的一部分毕业于她的ph。萨维尔博士和橡树岭国家实验室（ORNL），肯塔基大学和乔治亚州大学的教学和培训将由Savin博士和合作者进行监督。这项研究将导致学生的教育和培训成为未来的科学家。此外，这项工作还将增强萨维尔博士最近与ORNL合作者建立的研究和教育基础设施。测量将与ORNL科学家合作使用独特的ORNL设施进行。最后，为了增强科学和技术理解，该小组将在会议上广泛传播结果，并将其发布在适当的科学期刊中。***