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

这个项目的动机是由于在非常冷的白矮星中涉及H2分子的碰撞诱导吸收的现有计算的不足。这些恒星是我们银河系中最早一代恒星的遗迹，并构成了确定这一恒星群年龄的方法的基础。了解高密度、高温和频率下的碰撞诱导吸收光谱对于确定大气成分、有效温度、冷却速率和冷却年龄至关重要。在这里，由碰撞引起的致密氢气和氢氦混合物在1000到6000 K的温度和高达25000逆厘米的频率下吸收产生的不透明将从第一性原理计算出来。这些碰撞诱导的吸收系数将通过直接积分在光子存在下H2-X散射过程的Schrödinger方程得到，其中X = H2， He和/或H.除了二元吸收系数外，还将得到双加性成分和最强的远程不可约成分的三元吸收估计。三元配合物，如H2-H2-H2， H2-He-He和He-He-He - he，目前尚未解释，但已知是重要的，也将通过这项工作进行评估和提供。通过与Didier Saumon博士（洛斯阿拉莫斯国家实验室）和德克萨斯大学恒星大气小组（由Don Winget博士领导）的合作，这些新的碰撞诱导吸收计算将立即应用于非常冷的白矮星的大气建模。一些奇特的白矮星目前无法用现有的模型解释，希望在这里进行的工作将阐明这些问题。进一步预计，由新的碰撞引起的不透明所实现的分析能力将立即应用于许多其他领域，例如银河天文学和恒星演化。两名研究生将通过该项目获得支持，并在数值解的实现算法、密集数值计算、编程和测试方面接受培训。

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.