NVST望远镜高精度偏振光谱与矢量磁场的测量方法研究

For a proper understanding of the processes that leads to the variety of magnetic objects and features on the sun, it is necessary to measure the magnetic field vector with high precision. Spectro-polarimetric observations are widely operated at several solar telescopes. This propose is dedicated to the spectro-polarimetric observations of the New Vacuum Solar Telescope, using the multi-wavelength spectrograph. We aim to obtained and regularly provide the high-resolution vector magnetic field retrieved from full Stokes profiles of Fe I 532.4 nm. It involves a series of work such as the polarization calibration, the scanning observation mode, the inversion technique of the Stokes profiles, etc. This proposal will deeply study four areas following our previous work: (1) Study on the facticity and stability of the polarization calibration of the instrument. (2) Investigation on the optimization of the calibration method in order to improve the polarization accuracy. Combination with the modeling result provided by the theory model in order to build a dynamic calibration database. (3) Analysis of the two-dimensional spectro-polarization observation. (4) Magnetic field retrieval from the polarized spectrum. The characteristics and innovations of this proposal include the establishment of a specific polarimetric observation system for the NVST and the achievement of her capability to measure the vector magnetic field. This research can not only fill the gap in the field of the high-precision measurement of the magnetic field using a large-aperture telescope with a Alt-Az mount system, but also, considering the technique and experience implemented, can do contribution to the polarization analysis of the new generation solar instrument.

本项目旨在利用我国抚仙湖一米新真空太阳望远镜（New Vacuum Solar Telescope，NVST）多波段光谱仪开展偏振定标、光谱测量以及光球矢量磁场探测的研究工作。以能常规获得二维高精度矢量磁图为最终目标，系统研究磁场测量过程中的偏振定标、二维空间扫描、偏振轮廓反演等一系列问题。本项目主要在四个方面开展深入研究:(1) 实测定标方法准确性和稳定性的研究。(2) 优化定标方法提高偏振测量精度，同时与偏振建模相结合。(3) 活动区空间二维偏振光谱实测研究。(4) 偏振轮廓反演方法与光球磁场测量研究。项目特点和创新点包括: 建立了一套适用于NVST的高精度偏振光谱测量系统，实现NVST磁场测量功能，提升其科研能力和国际地位。同时填补我国在大口径地平式望远镜高精度磁场测量的空白。本项目在偏振光谱实测方面的经验和技术积累非常有利于我国其它需要高偏振精度的太阳磁场望远镜的偏振分析工作。

本项目依托我国抚仙湖一米新真空太阳望远镜（NVST）多波段光谱仪开展太阳偏振光谱观测与光球矢量磁场探测的研究工作。系统地研究了地平式望远镜在磁场测量过程中的仪器偏振定标、二维空间扫描、偏振信号反演等一系列问题。本研究主要在四个方面开展了深入: (1)仪器偏振特性的定标方法及方法的准确性和稳定性的研究。我们采用了基于偏振定标单元的实测定标方法，使用非线性最小二乘拟合方法获得望远镜偏振响应矩阵的全天变化情况，通过多次测量分析了方法的稳定性。我们的结论表明，实测定标方法可以较为准确地获得望远镜的偏振响应矩阵，可较准确地进行仪器偏振串扰的矫正。偏振测量精度 在10^(-3)量级。(2)优化定标方法提高偏振测量精度，同时与偏振建模相结合。实测定标方法的结果可以为建模定标方法提供有效的观测数据，使偏振建模更为准确。但目前偏振建模方法和拟合结果还有待于提高。(3)开展活动区空间二维偏振光谱实测研究。为了将AO系统接入多波段光谱仪我们升级改造了扫描机构，并进行了多次扫描测试。AO对于提高二维空间光谱观测的空间分辨率和偏振测量精度而言非常重要，需要大量的实战磨合。目前我们已经进行了多次带AO系统的二维空间扫描，发现若干问题，正在积极解决。(4)偏振轮廓反演方法与光球磁场测量研究。我们利用基于ME大气模型假设的反演程序，对定标后的偏振轮廓进行了反演。总结：在该项目的完成过程中，我们建立了一套适用于NVST的高精度偏振光谱测量系统，实现NVST磁场测量功能，提升了其科研能力和国际地位。为我国在大口径地平式望远镜高精度磁场测量方面积累了丰富的经验，培养了年轻的人才队伍。