[论文解读] Toward Next Generation Solar Coronagraph: Diagnostic Coronagraph Experiment

Kyung‐Suk Cho, Heesu Yang+9 more|arXiv (Cornell University)|Jun 11, 2020

Solar and Space Plasma Dynamics参考文献 1被引用 4

一句话总结

本文介绍了诊断日冕仪（DICE）的研制与验证，这是一种基于地面的太阳日冕冠状仪系统，通过在3934 Å和4305 Å波段进行窄带成像，用于测量低日冕区电子温度和速度。通过分析日冕中夫琅和费谱线的热展宽与多普勒频移，DICE成功生成了日面东侧边缘的温度分布图，显示日珥区温度较高，日冕洞边界温度较低，但日珥引起的散射污染了西侧边缘的数据。

ABSTRACT

Korea Astronomy and Space Science Institute (KASI) has been developing a next-generation coronagraph (NGC) in cooperation with NASA to measure the coronal electron density, temperature, and speed simultaneously using four different filters around 400 nm. KASI organized an expedition team to demonstrate the coronagraph measurement scheme and the instrumental technology through the 2017 total solar eclipse (TSE) across the USA. The observation site was in Jackson Hole, Wyoming, USA. We built an eclipse observation system, so-called Diagnostic Coronal Experiment (DICE), which is composed of two identical telescopes to improve a signal to noise ratio. The observation was conducted with 4 wavelengths and 3 linear polarization directions according to the planned schedule in a limited total eclipse time of about 140 seconds. Polarization information of corona from the data was successfully obtained but we were not able to obtain global information of coronal electron temperature and speed in the corona due to a low signal-to-noise ratio of the optical system and a strong emission from the prominence located in the western limb. In this study, we report the development of DICE and observation results from the eclipse expedition. TSE observation and analysis by using our own developed instrument gave an important lesson that a coronagraph should be carefully designed to achieve the scientific purpose of this study. And it was a very useful experience in the way for the success of follow-up NASA-KASI joint missions called the Balloon-borne Investigation of the Temperature and Speed of Electrons in the Corona (BITSE) and COronal Diagnostic EXperiment (CODEX).

研究动机与目标

• 开发一种基于地面的诊断日冕冠状仪系统，用于测量低太阳日冕区的电子温度和速度。
• 利用日全食作为试验平台，验证下一代日冕冠状仪的光学、滤光器和控制系统。
• 评估利用夫琅和费谱线的窄带成像技术推导日冕等离子体温度和径向速度的可行性。
• 识别未来空间任务（如CODEX）可能面临的系统性误差和技术挑战。

提出的方法

• 设计并集成一个紧凑的光学系统，包含50 mm口径镜头、通带滤光片、偏振片和CCD探测器。
• 实施由计算机控制的电动跟踪系统，以在日食期间保持太阳对准。
• 采用核心飞行系统（cFS）作为嵌入式控制软件，确保在时间关键条件下的可靠运行。
• 通过两个波段（3934 Å，对热展宽敏感；4305 Å，对多普勒频移敏感）的强度比实现温度与速度诊断。
• 在实验室条件下开展测试，验证系统分辨率（RMS光斑直径 <14.8 μm）和强度准确性（<±1%）在受控环境下的表现。
• 通过图像叠加和蒙特卡洛模拟提高信噪比，并估算温度不确定度。

实验结果

研究问题

• RQ1 在3934 Å和4305 Å波段对夫琅和费谱线进行窄带成像，能否准确反演低日冕区的电子温度和径向速度？
• RQ2 日珥引起的杂散光和镜头眩光在多大程度上影响日冕成像中温度测量的准确性？
• RQ3 日珥几何形状的不对称性（前表面与后表面）与对称模型相比，对温度比测量的影响有多大？
• RQ4 在标准公差分析中未被考虑的主导系统性误差有哪些？
• RQ5 cFS软件框架在实时控制便携式太阳日冕冠状仪系统方面的有效性如何？

主要发现

• DICE仪器成功生成了日冕东侧边缘的温度分布图，显示日珥区域温度较高，而与极区日冕洞交界处温度较低。
• DICE数据估算的温度与已知的日冕趋势一致，特别是在东侧边缘区域。
• 日珥引起的显著散射和镜头眩光导致西侧边缘区域温度测量不可靠。
• 观测到的比值变化超过了蒙特卡洛模拟预期的不确定度，表明存在未被考虑的系统性误差，如杂散光、衍射图样或平场校正问题。
• 日食期间一台相机发生故障，限制了数据采集，凸显了可靠电源分配和飞行前系统级测试的重要性。
• 使用cFS进行嵌入式控制被证明有效且可靠，支持未来类似系统在高空气球和空间任务中的部署。