Submilliarcsecond astrometry via VLBI. I - Relative position of the radio sources 3C 345 and NRAO 512

The relative position and relative proper motion of the radio sources 3C 345 and NRAO 512 were estimated from four sets of very-long-baseline interferometric observations, spaced between October 1971 and May 1974. Use of phase-connection techniques yielded the result ..cap alpha.. (3C345-NRAO 512) =2/sup m/ 29/sup s/.436 68 +- 0/sup s/.000 03 delta (3C345-NRAO 512) =1' 40''.726 3 +- 0''.000 3 for the separation in 1950.0 coordinates of the centers of brightness of the compact components of the two sources, and an upper bound of 0''.000 5 per year on their relative proper motion (70% estimated confidence limits).