使用US海军天文台天体照相仪和深度CCD成像的无线电-光学参考框架链接
Radio-Optical Reference Frame Link Using the US Naval Observatory Astrograph and Deep CCD Imaging
摘要：
在1997年至2004年期间，主要用0.9米CTIO进行了几次观测，对ICRF对应方（主要是类星体）进行成像，以确定准确的光学位置。当代这些深CCD图像相同的领域进行了观察与美国海军天文台（USNO）在同一带通的天体照相机。它们在依巴谷/第谷-2系统上提供了10至16星等范围内的恒星的精确位置，这些恒星被用作深层CCD成像数据的参考星。在这里，我们提出了最终的光学位置结果的413个来源的基础上获得的参考星专用天文观测减少以下2个不同的程序。这些光学位置进行了比较，无线电VLBI的位置。当前的光学系统与ICRF无线电系统没有完全对准，对于所有3个轴，在它们之间发现3到5质量（= 3西格玛水平）的刚体旋转角。此外，在统计上，光学减去无线电位置差异被发现超过总的，合并的，在观测中的已知误差。光学参考星位置的系统误差以及光学和无线电发射中心之间的物理偏移都被认为是可能的原因。一个有害的，天体物理，随机噪声（DARN）的组成部分被假定为约10质量的水平。如果未来的观测证实了这一点，这可能会严重限制盖亚与ICRF参考系的对准精度，使其在目前设想提供链接的源数量下，每个坐标轴的误差约为0.5质量。还提供了一个36个ICRF源的列表，这些源没有检测到大约R = 22的极限星等的光学对应物。
英文摘要：
Between 1997 and 2004 several observing runs were conducted mainly with the CTIO 0.9 m to image ICRF counterparts (mostly QSOs) in order to determine accurate optical positions. Contemporary to these deep CCD images the same fields were observed with the US Naval Observatory (USNO) astrograph in the same bandpass. They provide accurate positions on the Hipparcos/Tycho-2 system for stars in the 10 to 16 magnitude range used as reference stars for the deep CCD imaging data. Here we present final optical position results of 413 sources based on reference stars obtained by dedicated astrograph observations which were reduced following 2 different procedures. These optical positions are compared to radio VLBI positions. The current optical system is not perfectly aligned to the ICRF radio system with rigid body rotation angles of 3 to 5 mas (= 3 sigma level) found between them for all 3 axes. Furthermore, statistically, the optical minus radio position differences are found to exceed the total, combined, known errors in the observations. Systematic errors in the optical reference star positions as well as physical offsets between the centers of optical and radio emissions are both identified as likely causes. A detrimental, astrophysical, random noise (DARN) component is postulated to be on about the 10 mas level. If confirmed by future observations, this could severely limit the Gaia to ICRF reference frame alignment accuracy to an error of about 0.5 mas per coordinate axis with the current number of sources envisioned to provide the link. A list of 36 ICRF sources without the detection of an optical counterpart to a limiting magnitude of about R=22 is provided as well.
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