CTIO 0.9m observations of ICRF optical counterparts

摘要

We present astrometric results from 7 observing runs at the Cerro Tololo Interamer-jean Observatory (CTIO) 0.9m telescope of 197 extragalactic reference frame sources, selectedfrom the original International Celestial Reference Frame (ICRF) catalog. This is part of theU.S. Naval Observatory (USNO) reference frame link program. Contemporaneous to the CTIOdeep imaging, wide-field CCD data were taken with the USNO Twin Astrograph to provideaccurate secondary reference stars in the 13 to 16 mag range. The optical positions are on theHipparcos system (via Tycho-2 stars). The unweighted, mean RMS of positional differencesoptical—radio' for a single source is 28 and 25 mas for RA and Dec, respectively.