VLBA Observations of Radio Reference Frame Sources. III. Astrometric Suitability of an Additional 225 Sources

摘要: We present simultaneous dual-frequency Very Long Baseline Array 2 and 8 GHz observations of 225 the 560 extragalactic sources for which positions were reported by Johnston coworkers are now part International Celestial Reference Frame. These represent third final in a series intended to obtain single-epoch images entire set presented and, together with previously observations, bring total number observed 389. As previous papers this series, we use these data quantify magnitude expected effect intrinsic source structure on astrometric bandwidth synthesis Interferometry calculate "structure index" sources. The index can be used as an estimate quality Based indicator, correlations between radio position accuracy stability have been found. indicate that more extended larger uncertainties less positionally stable than compact