Collaborative Proposal: Opacity of Dense Hydrogen-Helium Gas Mixtures in White Dwarf Atmospheres

这个项目的动机是现有的关于碰撞诱导吸收的计算存在不足，这些吸收涉及非常冷的白矮星中的H2分子。这些恒星是我们银河系中最早一代恒星的遗骸，构成了确定这些恒星群体年龄的方法的基础。高密度、高温和频率下碰撞诱导吸收光谱的知识对于确定大气成分、有效温度、冷却速率和冷却时间至关重要。这里，将从第一原理计算在1000到6000 K和频率高达25,000逆厘米的密集氢气和氢-氦混合物中碰撞诱导吸收所产生的不透明度。这些碰撞诱导的吸收系数将通过直接积分光子存在下的H2-X散射过程的薛定谔方程得到，其中X=H2，He和/或H。除了二元吸收系数外，还将得到两两相加的分量和最强的长程不可约分量的三元吸收的估计。目前下落不明但已知重要的三元络合物，如H2-H2-H2、H2-He-He和He-He-He的贡献也将通过这项工作进行评估和提供。通过与洛斯阿拉莫斯国家实验室的Didier Saumon博士和由Don Winget博士领导的德克萨斯大学恒星大气小组的合作，这些新的碰撞诱导吸收计算将立即应用于对非常冷的白矮星的大气建模。目前有几个特殊的白矮星目前无法用现有的模型进行解释，希望在这里进行的工作将有助于阐明这些问题。进一步预计，由新的碰撞引起的不透明所带来的分析能力将立即应用于其他一些领域，如银河系天文学和恒星进化。两名研究生将通过这个项目得到支持，并在实施数值解、密集数值计算、编程和测试的算法方面进行培训。

This project is motivated by the inadequacy of existing calculations of collision-induced absorption involving H2 molecules in very cool white dwarfs. These stars are the remains of the earliest generation of stars in our Galaxy and form the basis for a method to determine the age of this stellar population. Knowledge of collision-induced absorption spectra at high densities, high temperatures and frequencies is crucial for the determination of atmospheric compositions, effective temperatures, cooling rates, and cooling ages.Here, opacities arising from collision induced absorption in dense hydrogen gas and hydrogen-helium mixtures at temperatures from 1000 to 6000 K and frequencies up to 25,000 inverse centimeters will be calculated from first principles. These collision-induced absorption coefficients will be obtained by direct integration of the Schrödinger equation of the H2-X scattering process in the presence of photons, with X = H2, He, and/or H. Besides the binary absorption coefficients, estimates of the ternary absorption of both the pairwise-additive components and the strongest long-range, irreducible components will be obtained. The contribution of ternary complexes such as H2-H2-H2, H2-He-He, and He-He-He, presently unaccounted for but known to be important will also be evaluated and made available through this work. Through collaboration with Dr. Didier Saumon (Los Alamos National Laboratory) and the Stellar Atmospheres Group at the University of Texas, headed by Dr. Don Winget, these new collision-induced absorption calculations will find immediate applications in the modeling of the atmospheres of very cool white dwarf stars.Several peculiar white dwarfs currently defy interpretation with current models and it is hoped that the work to be carried out here will shed light on these problems. It is further expected that the analysis capabilities enabled by the new collision-induced opacities will have immediate application in a number of other fields, such as Galactic astronomy and stellar evolution. Two graduate students will be supported through this project and trained in implementing algorithms for numerical solutions, intensive numerical computations, programming, and testing.