High Precision Relative Astrometry by Means of '4-Element' VLBI Observations

本研究旨在利用“四元”VLBI系统对近距离射电源同时进行的多视角差分VLBI观测，高精度地测量近距离射电源的相对位置。由于在这种观测方法中必须在很大程度上补偿大气和频率标准中出现的相位起伏的破坏性影响，因此可以预期获得非常精确的VLBI条纹和相位差作为观测值。为此，我们使用了野山射电天文台/NAO的45米毫米波望远镜和6米VLBI天线，以及通信研究实验室鹿岛空间研究中心的34米和26米天线，形成了长度约200公里的双基线。经过1992年3月和5月的三次预备实验，我们在6月27-28日成功地进行了主要的24小时观测，成功地进行了1992.10对角间隔为0.074度到10.35度的射电源以及一个引力透镜棒…观察到较多的Idate PKS1830-211。为了补偿信号传输系统内的相位延迟的影响，用两条基线交替地或通过切换到强校准源来观察每一对。在鹿岛使用K-3相关器进行的互相关处理表明，几乎所有震源都有良好的条纹，从而表明了4元素VLBI观测的基本可行性，并首次产生了一些多视角的VLBI差分数据。对数据进行了格式转换，并在水泽NAO大型计算机上进行了分析。结合实验，我们成功地建立了大气起伏对VLBI多视点差分观测影响的统计模型，表明在大气是精确观测的主要限制因素的情况下，高精度是可以实现的。对于相对较弱的射电源，我们还开发了一种有前景的长时间积分算法，并针对由于传输电缆失真而产生的相位延迟模型进行了研究。这些结果将用于解释分析的数据。较少

This research aims at measuring with high accuracy the relative positions of closely spaced radio sources by making use of simultaneous multi-view differential VLBI observations of those sources with '4-element' VLBI system. Since destructive effects of phase fluctuations occurring in the atmosphere and frequency standards must be largely compensated in this method of observations, one can expect to obtain very precise VLBI fringephase difference as an observable. For the purpose, we used 45-m mm-wave telescope and 6-m VLBI antenna at Nobeyama Radio Observatory/NAO, as well as 34-m and 26-m antennas at Kahshima Space Research Center of Communications Research Laboratory, forming dual baselines with length of about 200 km. After three preparatory experiments held in March and May of 1992, we successfully conducted the main 24-hour observations on June 27 - 28, 1992.10 pairs of radio sources with angular separation ranging from 0.074 to 10.35 degrees, as well as a gravitational lens cand … More idate PKS1830-211, were observed. Each pair was observed with two baselines alternately or by switching to a strong calibration source for the purpose to compensate the effects of the phase delay within the signal transmission systems. Cross-correlation processing carried out with K-3 correlator at Kashima revealed good fringes for almost all sources, thus showing the basic feasibility of the 4-element VLBI observations and yielding a number of multi-view differential VLBI data for the first time. The data were format-converted and now are analyzed on the main frame computer of NAO, Mizusawa.Along with the experiments, we successfully developed a statistical model of the atmospheric fluctuation effects upon the multi-view differential VLBI observations, and showed that the high accuracy is really achievable as far as the atmosphere is the primary limiting factor for the precise observations. We developed also an promising algorithm of long-time integration for relatively weak radio sources and models for phasedelays due to the distortion of the transmission cables. These results will be used in interpreting the analyzed data. Less