Formation of the helium extreme-UV resonance lines
Formation of the helium extreme-UV resonance lines
复制标题
氦极紫外共振线的形成
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
M. Carlsson
中科院分区：
文献类型：
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作者：
T. Golding;J. Leenaarts;M. Carlsson
上下文。虽然经典模型成功地再现了许多过渡区线的强度，但它们预测的极紫外（EUV）线强度大约比观测值低一个数量级。目标。我们的目的是确定氦EUV共振线的相关形成机制，能够解释在安静太阳条件下的高强度。方法。我们从三维辐射-磁流体动力学模拟模型中合成并研究了涌现谱。数值模拟自一致地考虑了日冕光照和氢、氦非平衡电离的影响。结果。辐射传递计算的结果是氦EUV线强度比经典假设下计算的强度大一个数量级。He i λ 584的增强主要是由He ii重组级联引起的。He ii λ 304和He ii λ 256的强度增强主要是由非平衡氦电离引起的。结论。分析表明，当考虑光学厚辐射转移和非平衡电离效应时，长期存在的高氦EUV谱线强度问题消失了。
Context. While classical models successfully reproduce intensities of many transition region lines, they predict helium extreme-UV (EUV) line intensities roughly an order of magnitude lower than the observed value. Aims. Our aim is to determine the relevant formation mechanism(s) of the helium EUV resonance lines capable of explaining the high intensities under quiet Sun conditions. Methods. We synthesised and studied the emergent spectra from a 3D radiation-magnetohydrodynamics simulation model. The effects of coronal illumination and non-equilibrium ionisation of hydrogen and helium are included self-consistently in the numerical simulation. Results. Radiative transfer calculations result in helium EUV line intensities that are an order of magnitude larger than the intensities calculated under the classical assumptions. The enhanced intensity of He i λ 584 is primarily caused by He ii recombination cascades. The enhanced intensity of He ii λ 304 and He ii λ 256 is caused primarily by non-equilibrium helium ionisation. Conclusions. The analysis shows that the long standing problem of the high helium EUV line intensities disappears when taking into account optically thick radiative transfer and non-equilibrium ionisation effects.