射电源结构效应对太阳系质心加速度估计的影响

The significant and continuing improvement in Astrometric/Geodetic observations has made the realization of Celestial Reference Frame (CRF) at the level of microarcsecond a reality and a necessity. The acceleration of the Solar system barycenter (SSB) causes celestial object an apparent proper motion with magnitude of about 5.8 microarcseconds per year and CRF a global distortion increasing with time. This phenomenon has become the most urgent effect needed to be handled with in CRF and Astrometric/Geodetic VLBI. The determination of the SSB’s acceleration from VLBI data analysis is the main work of the Ph.D. thesis of this project’s applicant and has obtained some important and interesting results. Extragalactic compact radio sources generally show structure with angular dimension of 0.2 – 20 milliarcseconds. Source structure effect is ignored so far in geodetic VLBI data analysis and thus is the major error source for the determination of the SSB’s acceleration. This project will continue the study of the determination of the SSB’s acceleration with more new data and different data analysis strategies, detect source structure based on the closure observables, and investigate the impact of source structure effect on the estimation of the acceleration. This project aims for the realization of the effect caused by the SSB’s acceleration in astrometry...Due to the significant contribution to the study of Galactic aberration caused by the SSB’s acceleration, the applicant of this project has been invited as a member of the International VLBI service for Astrometry and Geodesy (IVS) Working Group 8 “Galactic aberration”. With the help of this platform, we will broaden our research and enhance our achievement in the field. We are planning to finally submit a proposal of handling the effect to the ICRF group and IAU.

天体测量实测精度的不断提高，使得建立微角秒级精度的天球参考架成为必要和可能。忽略了太阳系空间加速度对运动学参考架的影响是当今作为国际参考标准的ICRF2所存在的重要缺陷，至今其累积影响已达亚毫角秒级并将继续扩大。用VLBI实测资料同时解算太阳系空间加速度参数和河外射电源的历元坐标是本项目申请人在博士期间的主要工作。天体测量中的致密射电源普遍表现出亚毫角秒水平的结构，成为太阳系质心加速度确定的主要误差源，研究该误差源的影响对银河系光行差效应在天体测量中的应用将起到推进作用。考虑到太阳系空间加速度所产生的多方面影响，精化太阳系质心加速度，探讨该参数的主要误差源—射电源结构效应的影响，和改进ICRF2的全面解决方案，是本项目的主要研究内容。.本项目申请人受邀成为IVS银河系光行差工作组的成员，借助这一平台，进行该项目的研究将是我们保持国际研究前沿的重要和难得的机遇。

本项目立项（2017年1月）正值全球组建下一代VLBI台战网（VGOS）和开展VGOS实验性观测之际，全球目前已建成近20台VGOS超快速旋转、超宽频（2-14GHz）的小天线，朝着1 mm地球参考架台站位置精度和0.1 mm/yr的台站稳定性目标迈进。本项目的研究证实射电源结构效应的影响是实现天球参考架长期稳定性的关键和VLBI观测中主导的误差源，直接制约下一代VGOS计划的发展。本项目围绕射电源结构效应展开系统和深入的研究，主要包括VLBI观测数据中射电源结构效应的探测方法，对测地观测结果和估计参数的影响分析，和射电源结构效应进行改正的原理方法等方面进行探索性研究，进而对VLBI观测估计太阳系质心加速度结果中射电源结构效应的影响有定量的分析。截止2019年底，本项目组成员已经顺利完成了项目的全部目标，取得在国际上具有相当影响的成果，发表了数篇重要的文章，并将最终的研究结论写入国际VLBI组织（IVS）的第八工作组——IVS galactic aberration working group发表在A&A上的题为“Galactocentric acceleration in VLBI analysis. Finding of IVS WG8”的总结论文中。本项目还将研究方法应用在下一代VGOS观测中，获得了超出原计划的研究成果，并将会对VGOS的数据处理产生深远影响和指导意义。

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