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

原子氢单电荷和双电荷的热能电荷转移(CT)在决定行星状星云、H II区、LYA云、星系间介质(IGM)以及超新星遗迹和HerBig-Haro天体的电离结构、热结构、发射光谱和吸收光谱等方面起着重要作用。对这些源的地面光谱观测被用来解决天体物理学中的许多基本问题，如原始氦丰度、宇宙的化学演化、作为红移函数的超银河辐射场的形状、星系化学演化和恒星核合成。要解决这些问题尤其重要的是C、N和O的单电荷和双电荷离子的可靠热能CT率系数。天体物理学中使用的大多数热CT数据都是用Landau-Zener(LZ)方法计算的。丹尼尔·沃尔夫·萨文博士的实验室结果表明，热CT截面的LZ计算误差可达一个数量级。还存在一些最先进的分子轨道紧密耦合(MOCC)计算。但实验室工作表明，如果没有基准测量，MOCC热CT截面计算的误差可能高达3.DR倍。Savin和他的同事将开展一个实验室测量和模拟研究相结合的计划，对热能下C2+、N+、N2+、O+和O2+在原子H上的CT进行研究。他们已经对C++进行了这样的测量。新的测量将使用橡树岭国家实验室的离子原子合束装置进行，这是现有的唯一能够进行拟议的热能截面测量的设备。结果将用于基准最先进的MOCC计算。这些测量，如果需要，结合基准理论，也将被用来产生CT率系数，估计精度为20%。该小组将发布对导出的速率系数的简单拟合，以便天体物理界可以在他们的宇宙等离子体研究中使用新数据。在进行测量的同时，他们将使用云进行建模研究，以调查新数据的天体物理含义，以及由于未测量的CT数据中对其他离子的任何推断的不确定性而产生的含义。一些有待研究的问题包括CT在确定用于从H II区推断原始He丰度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，这些观测被用来限制宇宙的化学演化和作为红移函数的元银河辐射场的形状。这项研究项目的很大一部分将由哥伦比亚大学的一名毕业生完成，部分满足她/他的博士要求。学生的教学和培训将由Savin博士和橡树岭国家实验室(ORNL)、肯塔基大学和佐治亚-雅典大学的合作者监督。因此，这项研究将导致对学生进行教育和培训，使其成为未来的科学家。此外，这项工作将加强哥伦比亚/ORNL的研究和教育基础设施，这是萨文博士最近与他在ORNL的合作者建立的。这些测量将与ORNL的科学家合作，使用独特的ORNL设备进行。最后，为增进对科学和技术的了解，专家组将在各次会议上广泛传播这些成果，并在适当的科学期刊上发表。

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.***