[论文解读] Hot prominence detected in the core of a Coronal Mass Ejection: III. Plasma filling factor from UVCS Lyman-$α$ and Lyman-$β$ observations

Roberto Susino, А. Бемпорад+2 more|arXiv (Cornell University)|May 31, 2018

Solar and Space Plasma Dynamics参考文献 27被引用 10

一句话总结

本研究提出一种方法，利用SOHO/LASCO-C2（可见光）与SOHO/UVCS（紫外）对Lyman-α和Lyman-β发射的同步观测，估算喷发日珥中视线方向的等离子体填充因子。通过将共振散射与碰撞激发模型结合热力学参数，并基于一维非局部热动平衡（non-LTE）辐射转移模型，作者推导出与模型一致的填充因子，显示对流速的敏感性较弱，但对动能温度的依赖性较强，验证了该技术在光学薄发射条件下的适用性。

ABSTRACT

This work deals with the study of an erupting prominence embedded in the core of a CME and focuses on the derivation of the prominence plasma filling factor. We explore two methods to measure the prominence plasma filling factor that are based on the combination of visible-light and ultraviolet spectroscopic observations. Theoretical relationships for resonant scattering and collisional excitation are used to evaluate the intensity of the H I Lyman-α and Lyman-β lines, in two prominence points where simultaneous and cospatial LASCO-C2 and UVCS data were available. Thermodynamic and geometrical parameters assumed for the calculation are provided by both observations and the results of a detailed 1D non-LTE radiative-transfer model of the prominence, developed in our previous work (Heinzel 2016). The filling factor is derived from the comparison between the calculated and the measured intensities of the two lines. The results are then checked against the non-LTE model in order to verify the reliability of the methods. The resulting filling factors are consistent with the model in both the prominence points when the separation of the radiative and collisional components of the total intensity, required to estimate the filling factor, is performed using both the line intensities. An exploration of the parameter space shows that the results are weakly sensitive to the plasma velocity, but they depends more strongly on the assumed kinetic temperatures. The combination of visible-light and ultraviolet Lyman-α and Lyman-β data can be used to approximately estimate the geometrical filling factor in erupting prominences, but the proposed techniques are reliable only for emission that is optically thin in the lines considered, condition that is not in general representative of prominence plasma.

研究动机与目标

• 开发一种依赖于模型的方法，利用紫外与可见光观测估算喷发日珥中视线方向的几何填充因子。
• 检验结合Lyman-α与Lyman-β强度及可见光偏振亮度（pB）以推断填充因子的可靠性。
• 评估该方法对关键等离子体参数（如流速与动能温度）的敏感性。
• 通过与日珥结构的一维非-LTE辐射转移模型对比，验证该方法的有效性。
• 提供一种实用的初步估算工具，用于日珥中等离子体参数的估计，以指导更详细的建模。

提出的方法

• 利用中性氢Lyman-α与Lyman-β线共振散射与碰撞激发的理论关系。
• 采用观测与模拟的热力学及几何参数：电子柱密度、动能温度、流速、色球层谱线强度以及视线方向的日珥厚度。
• 通过强度比分析，将计算的Lyman线强度与实测的UVCS与LASCO-C2强度进行比较，推导填充因子。
• 应用两种方法：一种基于利用Lyα与Lyβ强度分离辐射与碰撞线成分。
• 将结果与先前研究（Heinzel et al. 2016）中的一维非-LTE辐射转移模型进行验证，确保一致性。
• 开展参数空间探索，评估对流速与动能温度的敏感性，使用多普勒减弱因子与线轮廓假设。

实验结果

研究问题

• RQ1 结合UVCS的Lyman-α与Lyman-β强度及LASCO-C2的pB观测，能否可靠估算日珥等离子体填充因子？
• RQ2 所推导的填充因子对等离子体流速与动能温度的不确定性有多敏感？
• RQ3 关于色球层谱线轮廓与非热运动的假设在多大程度上影响填充因子的估算？
• RQ4 该方法在典型日珥等离子体的光学薄发射条件下是否具有鲁棒性？
• RQ5 该方法能否为更详细的建模提供可靠的初步参数估计？

主要发现

• 当利用Lyα与Lyβ数据分离Lyman线强度的辐射与碰撞成分时，所推导的填充因子在两个日珥点均与非-LTE模型结果一致。
• 该方法对假设的等离子体流速仅表现出微弱依赖性，在100–300 km s⁻¹的速度范围内，强度比F(α)/F(β)的变化小于30%。
• 填充因子估算对假设的动能温度更为敏感，这会影响碰撞系数与电离分数。
• 有效温度（与线轮廓宽度相关）的变化对填充因子的影响小于15%，表明该参数的敏感性较低。
• 该方法仅在光学薄发射条件下可靠，而这一条件通常不具代表性，限制了其普遍适用性。
• 该技术可提供填充因子的可靠一阶估算，并可作为更详细日珥参数建模的初始猜测。