A RADIO OPTICAL REFERENCE FRAME .2. ADDITIONAL RADIO AND OPTICAL SOURCE POSITIONS IN THE NORTHERN-HEMISPHERE

VLBI observations from 12 sessions have been made of a total of 103 sources north of - 2-degrees declination. These data give the first extension to the radio/optical reference frame catalog already defined by the data in the NASA Crustal Dynamics Project database prior to July 1988 [Ma et al., AJ, 90, 1284 (1990)]. The new observations add 53 new sources to the radio reference frame catalog, improve the positions of 29 from the previous version, and show another seven sources to be unsuitable reference frame objects. Observations of 14 calibration sources tie the new positions to the existing catalog. The formal mean errors for the radio positions of the additional sources are about 0.8 mas in each coordinate. Optical positions for eight sources have been measured in the FK5 system, bringing the total number of sources in the catalog with accurate positions for their optical counterparts to 36. The new optical positions have an accuracy of about 50 mas.