EXTRAGALACTIC OPTICAL-RADIO LINK RESEARCH AT USNO

Over 500 counterparts of ICRF sources were observed during 24 deep CCD observing runs as part of the USNO CCD Astrograph Catalog (UCAC) project, providing a direct link to Tycho-2 stars. For some sources a positional accuracy of 10 mas is achieved. A sample of 12 extragalactic ICRF sources are being observed at the Naval Observatory Flagstaff Station (NOFS) 1.55-meter telescope over several years to monitor optical position stability. First high resolution imaging of selected sources are obtained at the Lick 3-meter AO system to correlate source structure with optical-radio centroid offsets. As part of the Space Interferometry Mission (SIM) preparatory science about 240 bright QSO's are monitored for photometric variability in B,V,R and I. The USNO Robotic Astrometric Telescope (URAT) will be able to combine deep CCD imaging of all ICRF2 target areas and millions of compact galaxies with a stellar, astrometric, all-sky survey of multiple epochs.