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arXiv 2406.11297astro-ph.SR
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参数对模拟日冕物质抛射及其驱动激波的 H I Lyα 谱线总强度的影响

Parameter effects on the total intensity of H I Lyα line for a modelled coronal mass ejection and its driven shock

Beili Ying, Guanglu Shi, Li Feng, Lei Lu, Jianchao Xue, Shuting Li, Weiqun Gan, Hui Li

AI总结:

本文通过三维MHD模拟CME及其驱动激波,系统评估了盘面Lyα入射强度、几何散射函数和动力学温度假设对理论Lyα强度的影响,发现不同假设在CME不同区域产生差异化的高估或低估误差。

摘要:

将 H I Lyα(121.6 nm)谱线形成机制与紫外(UV)Lyα 和白光(WL)观测相结合,为确定日冕物质抛射(CMEs)的电子温度提供了一种有效方法。确保该诊断技术准确性的关键在于精确计算理论 Lyα 强度。本研究通过三维磁流体动力学(3D MHD)模拟,构建了一个模拟的日冕物质抛射及其驱动的激波。我们生成了该 CME 和激波的合成紫外与白光图像,以量化不同假设对理论 Lyα 强度的影响,这些假设包括 Lyα 谱线的入射强度(Idisk)、几何散射函数(p(θ))以及假设与质子温度(Tp)或电子温度(Te)相等的动力学温度(Tn)。通过比较这些假设下 Lyα 强度的差异,我们发现:(1)与同步图相比,使用均匀盘面或卡林顿(Carrington)图作为盘面 Lyα 发射源会低估日冕 Lyα 强度(< 10%),但在部分 CME 核心区域存在轻微高估(< 4%)。卡林顿图产生的误差小于均匀盘面。(2)几何散射过程对 Lyα 强度的影响较小,最大相对误差小于 5%。大部分区域 Lyα 强度被低估,但在 CME 核心区域被高估。(3)与假设 Tn = Tp 相比,采用 Tn = Te 会导致 CME Lyα 强度的相对误差更加复杂。CME 核心和暗腔均被高估,核心区域的最大误差超过 50%,暗腔区域保持在 35% 以下。在 CME 前沿,同时存在高估和低估,相对误差小于 35%。电子温度假设对激波的影响较小,低估的相对误差小于 20%。

英文摘要:

The combination of the H I Lyα (121.6 nm) line formation mechanism with ultraviolet (UV) Lyα and white-light (WL) observations provides an effective method for determining the electron temperature of coronal mass ejections (CMEs). A key to ensuring the accuracy of this diagnostic technique is the precise calculation of theoretical Lyα intensities. This study performs a modelled CME and its driven shock via the 3D MHD simulation. We generate synthetic UV and WL images of the CME and shock to quantify the impact of different assumptions on theoretical Lyα intensities, such as the incident intensity of the Lyα line (Idisk), the geometric scattering function (p(θ)), and the kinetic temperature (Tn) assumed to be equal to the proton (Tp) or electron (Te) temperatures. By comparing differences of the Lyα intensities under these assumptions, we find that: (1) Using the uniform or Carrington maps of the disk Lyα emission underestimates the corona Lyα intensity (< 10%) compared to the synchronic map, except for a slight overestimate (< 4%) in the partial CME core. The Carrington map yields lower uncertainties than the uniform disk. (2) The geometric scattering process has a minor impact on the Lyα intensity, with a maximum relative uncertainty of < 5%. The Lyα intensity is underestimated for the most part but overestimated in the CME core. (3) Compared to the assumption Tn = Tp, using Tn = Te leads to more complex relative uncertainties in CME Lyα intensity. The CME core and void are both overestimated, with the maximum uncertainty in the core exceeding 50% and the void remaining below 35%. In the CME front, both over- and under-estimates exist with relative uncertainties of < 35%. The electron temperature assumption has a smaller impact on the shock, with an underestimated relative uncertainty of less than 20%.

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