Program: GN-2011B-Q-109

More than 1000 radio quasars are observed regularly by the International VLBI Service, IVS, to define and maintain the International Celestial Reference Frame, ICRF. Using these data we have presented evidence for large scale proper motions. While the dipole effect is consistent with theoretical prediction, the quadrupole effect, at a level in excess of 10 muas/year, may present a serious challenge to the standard cosmologies. More VLBI observations for the high redshift radio sources are required to improve accuracy of the quadrupole effect estimates. The new SDSS release provides a rare opportunity to achieve that using the five colour photometry data. Combining the red excess objects from the SDSS and the flat spectrum radio sources observed by geodetic VLBI, we preselected 23 targets to measure their redshift with GMOS on the Gemini North telescope. These objects are spread uniformly in the right ascensions and all have unique optical identifications based on precise radio-optical position coincidence. A dedicated 5-year VLBI program for astrometry of these potential high redshift quasars will be launched during 2011.