Astrometry of millijansky sources using a phase reference VLBI technique

A technique for the reliable VLBI detection of weak (mJy at cm wavelengths) celestial radio sources such as radio stars, fast pulsars, and faint extragalactic objects is described and demonstrated. The coherence time is increased by observing a strong phase-reference source alternately with the program source, thus providing an accurate astrometric position relative to the reference source. Typical results are presented in tables, graphs, and a contour map and briefly characterized.