Showing papers by "John Reynolds published in 1994"

A Radio Optical Reference Frame. VII. Additional Source Positions From a Southern Hemisphere Short Baseline Survey

Abstract: We report accurate radio positions for 107 VLBI sources using Very Long Baseline Inteferometry (VLBI), as part of a continuing program to establish a global reference frame of about 400 extragalactic radio positions. The observations were made with Australian radio telescopes at Tidbinbilla and Hobart during 1990 using Mark III VLBI recording systems. The positions reported here add 50 new sources to the global reference frame catalog, bringing the total number to 403, of which 208 are in the Northern hemisphere and 195 in the Southern. The new positions have median errors of about 5 milliarseconds, limited by the relatively short baseline of 832 km.

A radio/optical reference frame. 5: Additional source positions in the mid-latitude southern hemisphere

Abstract: We report new accurate radio position measurements for 30 sources, preliminary positions for two sources, improved radio postions for nine additional sources which had limited previous observations, and optical positions and optical-radio differences for six of the radio sources. The Very Long Baseline Interferometry (VLBI) observations are part of the continuing effort to establish a global radio reference frame of about 400 compact, flat spectrum sources, which are evenly distributed across the sky. The observations were made using Mark III data format in four separate sessions in 1988-89 with radio telescopes at Tidbinbilla, Australia, Kauai, USA, and Kashima, Japan. We observed a total of 54 sources, including ten calibrators and three which were undetected. The 32 new source positions bring the total number in the radio reference frame catalog to 319 (172 northern and 147 southern) and fill in the zone -25 deg greater than delta greater than -45 deg which, prior to this list, had the lowest source density. The VLBI positions have an average formal precision of less than 1 mas, although unknown radio structure effects of about 1-2 mas may be present. The six new optical postion measurements are part of the program to obtain positions of the optical counterparts of the radio reference frame source and to map accurately the optical on to the radio reference frames. The optical measurements were obtained from United States Naval Observatory (USNO) Black Birch astrograph plates and source plates from the AAT, and Kitt Peak National Observatory (KPNO) 4 m, and the European Southern Observatory (ESO) Schmidt. The optical positions have an average precision of 0.07 sec, mostly due to the zero point error when adjusted to the FK5 optical frame using the IRS catalog. To date we have measured optical positions for 46 sources.