Using a small subset of the compact extragalactic radio sources that are monitored in at 13 cm and 3.6 cm in the framework of the maintenance of the International Celestial Reference Frame ICRF, we showed that detailed reliable position information can be derived since the late 1980's, with a 0.5 year resolution. The study is restricted to sources north of +20 degrees in declination, to avoid a possible contribution of the propagation delay due to the wet troposphere to the apparent stability in declination. The analysis shows that the time variability of these objects have varied spectral characteristics, that could possibly be related to diversified physical processes.
© European Southern Observatory (ESO) 2000
Online publication: July 13, 2000