Precise Positions of Radio Sources. II. Optical Measurements

Optical positions of forty-one identified radio sources have been measured on 48-inch Schmidt plates or, where crowded or faint, on 200-inch plates. Reductions were made relative to an average of twenty-one standard stars within 1 of each source position. Positions of the standards were updated by proper-motion corrections to the epoch of each plate, retaining the equinox of 1950.0. Internal rms errors average 0'13 in each coordinate. The positions, listed in a table, are on the system of the AGK3, which itself is on the FK4 system. Six new optical identifications have been made. NRAO 140, PKS 1508-05, and 3C 343 are probably QSSs. The first t'vo are bright (mpg 17, and mpg 16). The image of 3C 343 is exceedingly faint (V 22) and may be connected by a bridge (unconfirmed) to a nearby twenty-first magnitude galaxy which itself is a member of a small group. The remaining three new identifications (3C 256, 3C 343.1, and NRAO 530) are probably galaxies, with a possibility that the last is in a cluster. Two previously suggested identifications (3C 256,0056-17) are found to be incorrect. Six fields remain empty brighter than fltpg 21.0. Of these, PKS 2127+04 is particularly interesting because a cluster of galaxies may be present near the radio position just at the plate limit but so faint as to be unmeasurable on the Schmidt blue plates. No confirmatory 2004nch plates are yet available.