The third iteration of the International Celestial Reference Frame (ICRF3) is made up of 4536 quasars observed at S/X bands using Very Long baseline Interferometry (VLBI). These sources are high redshift quasars, typically between $1<z<2$, that are believed to host active galactic nuclei (AGN) at their centers. The position of compact radio sources can be determined better than sources with large amounts of extended radio structure. Here we report information on a series of 20 observations from January 2017 through December 2017 which were designed for precise astrometry and to monitor the structure of sources included in the ICRF3. We targeted 3627 sources over the one year campaign and found the median flux density of 2697 detected sources at S-band is 0.13 Jy, and the flux density of 3209 sources detected at X-band is 0.09 Jy. We find that $70\%$ of detected sources in our campaign are considered compact at X-band and ideal for use in the ICRF and $89\%$ of the 2615 sources detected at both frequencies have a flat spectral index, $α>0.5$
VLBI astrometry of radio stars to link radio and optical celestial reference frames - II. 11 radio stars
Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Department of Geodesy and Geodynamics, Finnish Geospatial Research Institute (FGI), National Land Survey of Finland（芬兰国家土地测量局芬兰地理研究所大地测量与地球动力学系）；Korea Astronomy and Space Science Institute（韩国天体物理与空间科学研究所）；University of Helsinki（赫尔辛基大学）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密森尼天体物理中心）
Absolute Motion of the Infrared Counterpart to Sagittarius A* in the Gaia Celestial Reference Frame 3 and Limits on an Intermediate-mass Black Hole Companion
University of California, Los Angeles（加州大学洛杉矶分校）；University of Nevada, Reno（内华达大学里诺分校）
Gaia Data Release 1: The reference frame and the optical properties of ICRF sources
作为Gaia DR 1数据处理的一部分，计算了一个特殊的天体测量解，即所谓的辅助类星体解。这给出了选定的河外天体的位置，包括国际天体参考系（ICRF 2）第二次实现中的射电源，这些射电源具有足够明亮的光学对应物，可以与盖亚一起观察。这些位置的子集用于将Gaia DR 1的位置参考系与ICRF 2对齐。我们描述的盖亚辅助类星体的解决方案的一个子集的源匹配ICRF 2的属性，并比较它们的光学和无线电的位置在亚质量水平。50%的源的形式标准误差优于0.76毫角秒（mas），90%的源的形式标准误差优于3.35毫角秒。光学星等是在盖亚未过滤的光度G波段获得的。与定义源的无线电位置的比较表明，系统差异不大于零点几个mas。有问题的解决方案的分数，不容易占统计，是小于6%。标准化的差异延长了尾部，需要对大约100个源进行逐案调查，但我们还没有看到任何与源中的光无线电偏移有关的差异。
