H, He-like recombination spectra I : l-changing collisions for hydrogen
H, He-like recombination spectra I : l-changing collisions for hydrogen
复制标题
H，类 He 重组光谱 I：氢的 l 变化碰撞
DOI：
10.1093/mnras/stw893
复制
发表时间：
2016
影响因子：
4.8
通讯作者：
G. Ferland
中科院分区：
文献类型：
--
作者：
F. Guzm'an;N. Badnell;R.J.R. Williams;P. V. Hoof;M. Chatzikos;G. Ferland
星云中的氢和氦发射线是由辐射复合形成的。这是一个简单的过程，原则上可以非常精确地描述。He I和H I发射线的比值可以用来测量He+/H+丰度比，其精度与复合速率系数相同。本文研究了关于描述n壳层内能量简并态偶极变l碰撞（nl → nl 0 = l ±1）的正确理论的争论。半个世纪以来，彭盖利和西顿（1964）的工作一直被认为是“解决”了这个问题的权威性研究。Vrinceanu等人（2012年）最近的工作建议使用半经典近似的速率系数，其比Pengelly & Seaton（1964年）的速率系数小近一个数量级，结果是需要显著更高的密度才能使nl种群达到局部热力学平衡。在这里，我们比较预测的H I发射率从两个作品，并发现广泛的差异，高达10%。这远远超过了从观测中获得原始He/H丰度比所需的1%精度，从而限制了大爆炸宇宙学。我们推荐使用Pengelly & Seaton（1964）的变l碰撞速率系数来描述H复合谱，这是基于长程偶极相互作用的量子力学表示。
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple process which, in principle, can be described to very high precision. Ratios of He I and H I emission lines can be used to measure the He+/H+ abundance ratio to the same precision as the recombination rate coefficients. This paper investigates the controversy over the correct theory to describe dipole l-changing collisions (nl → nl0 = l ±1) between energy-degenerate states within an n-shell. The work of Pengelly & Seaton (1964) has, for half-a-century, been considered the definitive study which “solved” the problem. Recent work by Vrinceanu et al. (2012) recommended the use of rate coefficients from a semi-classical approximation which are nearly an order of magnitude smaller than those of Pengelly & Seaton (1964), with the result that significantly higher densities are needed for the nl populations to come into local thermodynamic equilibrium. Here, we compare predicted H I emissivities from the two works and find widespread differences, of up to ≈ 10%. This far exceeds the 1% precision required to obtain the primordial He/H abundance ratio from observations so as to constrain Big Bang cosmologies. We recommend using the rate coefficients of Pengelly & Seaton (1964) for l-changing collisions, to describe the H recombination spectrum, based-on their quantum mechanical representation of the long-range dipole interaction.