RORF - a Radio Optical Reference Frame
  The radio observations are based on dual frequency Mark--III VLBI data from 1979 until the end of 1993. Currently 436 sources define the celestial inertial frame. A comparison to the JPL94R01 catalog is made. Position vs. time plots of selected sources show significant apparent non linear proper motions. The status of the project and recent results from optical observations are presented. 
N.Zacharias, A.L.Fey, J.L.Russell and K.J.Johnston