CCD OBSERVATIONS LINKING THE RADIO AND OPTICAL REFERENCES FRAMES

Observations made with the U.S. Naval Observatory 20 cm transit telesc ope are presented for 104 FK5 and 13 radio stars that are directly tie d into the J2000 extragalactic reference system. A comparison of the s tar positions presented in this paper with the FK5 catalog finds possi ble warps in the FK5 reference system with amplitudes approximately 0. 1 arcsec and rotations for linking the optical and radio reference sys tems with values omega(x) = -20 +/- 17 (s.e.), omega(y) = 28 +/- 16 (s .e.), and omega(z) = 11 +/- 13 (s.e.) mas. When the data of this paper are combined with other studies, these rotations become omega(x) = 11 +/- 13 (s.e.), omega(y) = 40 +/- 13 (s.e.), and omega(z) = 17 +/- 9 ( s.e.) mas, indicating the omega(y) rotation might be real. Among the r adio stars, there are four stars (KQ Pup, 54 Cam, SZ Psc, and HD 24408 5) with significant optical-radio offsets that exceed 0.15 arcsec in m agnitude. Moreover, many other radio stars probably have appreciable o ffsets as determined from a statistical investigation. Optical-radio o ffsets which are typically accurate to sigma approximately +/-42 (s.e. ) mas are also presented for 48 extragalactic objects observed with th e transit telescope. Among these objects, 21% have significant offsets . Radio galaxies are much more likely to have large offsets than QSOs and BL Lac objects, making many of them poor candidates for radio refe rence objects.