The Second Realization of the International Celestial Reference Frame (ICRF2) by Very Long Baseline Interferometry

The XXVIIth General Assembly of the IAU recently voted to adopt the second realization of the International Celestial Reference Frame (ICRF2) as the fundamental astrometric reference frame, effective 01 January 2010. ICRF2 contains precise positions of 3414 compact radio astronomical sources, more than five times the number as in the first realization of the ICRF (ICRF1). Furthermore, ICRF2 is found to have a noise floor of approximately 40 microarcseconds, some 5-6 times better than ICRF1. The axis stability of the frame is roughly 10 microarcseconds, nearly twice as stable as ICRF1. Alignment of ICRF2 with the International Celestial Reference System (ICRS) was achieved using 138 stable sources common to both ICRF2 and ICRF-Ext2. Future maintenance of ICRF2 will be accomplished using a set of 295 new "defining" sources selected on the basis of positional stability and the lack of extensive intrinsic source structure. Here we present relevant details regarding the data, modeling, testing and validation of the ICRF2 catalog, and its alignment onto the ICRS.