Preparations for the next ICRF

D. Gordon1 and D. MacMillan1

1NVI Inc./NASA GSFC Code 698, USA

Oral presentation

The second implementation of the International Celestial Reference Frame (ICRF2) is scheduled to be presented to the IAU for approval later this year. Towards that goal, an IERS/IVS working group has been busily preparing for its generation. Some deficiencies of the first ICRF were a shortage of reference frame 'defining' sources in the far southern sky and that a small fraction of the defining sources turned out to be unstable over time. To overcome those deficiencies, members of the ICRF2 working group have studied the temporal history of the VLBI sources and rated them with respect to their degree of stability. Several prospective lists of 'defining' sources have been generated and will be merged together. Numerous test solutions have been generated to determine the uncertainties and noise levels in the catalogs and to determine the best set of data and models to use for the final catalog. We will discuss various methods used to rank the stability of the sources and will also present results from some of the test catalog solutions, such as effects of atmosphere gradients, pressure loading, thermal deformation, use of correlated noise, and other effects.