The Position Stability of Compact Radio Sources at 23 and 43 GHz

K. Johnston, D. Boboltz, A. Fey, E. Fomalont

The registration accuracy between the radio ICRF and optical catalogs that will be produced from earth-orbiting telescopes may be limited by the intrinsic stability of the compact objects that are common to the radio and optical skies.  As a first step in the determination of the radio stability, we have chosen four ICRF radio sources that lie within a three-degree region in order to use phase referencing to monitor the changes in structure and apparent position among the sources.  We began observations in late 2008 at 23 GHz with the Japanese VERA array and at 23 GHz and 43 GHz with the VLBA, and will observe the four sources at various time intervals over one year. Our first two VLBA sessions in Dec 2008 were separated by two days, and we report on the comparison of the structures and positions.  The initial results suggest that the positional accuracy in the east/west direction is about 15 μas, and that the structures for two of the four sources are surprisingly complex at 23 and 43 GHz.