MULTI-STEP VLBI OBSERVATIONS OF WEAK EXTRAGALACTIC RADIO SOURCES TO ALIGN THE ICRF AND THE FUTURE GAIA FRAME
MULTI-STEP VLBI OBSERVATIONS OF WEAK EXTRAGALACTIC RADIO SOURCES TO ALIGN THE ICRF AND THE FUTURE GAIA FRAME
复制标题
对弱河外无线电源进行多步 VLBI 观测，以协调 ICRF 和未来的盖亚框架
DOI：
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发表时间：
2008
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通讯作者：
S. Garrington
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作者：
G. Bourda;P. Charlot;R. Porcas;S. Garrington
空间天体测量使命盖亚将建立一个密集的光学类星体为基础的天体参考框架。为了使光学和无线电位置保持一致，必须以最高的精度将盖亚框架和国际天球参考框架（ICRF）对准。目前，发现只有10%的ICRF源适合建立这种联系，要么是因为它们在光波长下不够明亮，要么是因为它们具有显著的扩展无线电发射，这妨碍了达到最高的天体测量精度。为了改善这种情况，我们已经启动了一项VLBI调查，致力于寻找额外的合适的无线电源，使两个框架对齐。样本由大约450个源组成，通常比目前的ICRF源弱20倍（低至20 mJy通量水平），这些源是通过互相关光学和无线电目录选择的。本文提出了观测策略，以检测，成像，并测量这些源的准确位置。它还将提供2007年6月和10月通过欧洲VLBI网络进行的初步观测得出的关于源的VLBI可探测性的结果。基于这些观察，发现89%的极好的检测率，这对于该项目的继续是非常有希望的。
The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia frame and the International Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is found that only 10% of the ICRF sources are suitable to establish this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of about 450 sources, typically 20 times weaker than the current ICRF sources (down to the 20 mJy flux level), which have been selected by cross-correlating optical and radio catalogues. This paper presents the observing strategy to detect, image, and measure accurate positions for these sources. It will also provide results about the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, an excellent detection rate of 89% is found, which is very promising for the continuation of this project.