Quasr link conditions for Hipparcos.
Ducourant, C.; Brosche, P.; Geffert, M.; Galas, R.; Karafistan, A.
Germany
Abstract
Fictitious proper motions of quasars and of their surrounding stars have been determined based on plates with epoch differences of up to 90 yrs. From the fact that the true proper motions of the quasar are vanishingly small, we obtain conditions for the extragalactic calibration of the preliminary Hipparcos system. We present results for the fields of 3C 273, OQ 208, 3C 371 and 3C 390.3. With these data it is possible to achieve the link with random errors smaller than 0.15'' per century.