N-Cat Series Combined Extragalactic Radio Source Catalogues

The N-Cat series combined extragalactic radio source catalogues were compiled on the bases of the Arc Length Difference primary source selection method and the Common Primary Source orientation maintenance model, and by reference to the correlations among individual catalogues. Tests show that the Arc Length Difference selection method can highlight the individuality of every source on the basis of consistence of all sources and can be adapted to the improvement in the accuracy of observation catalogues, the sky coverage and so on.It is relatively an objective selection method. Calculations show that the Common Primary Source orientation maintenance model is more desirable than the IERS one, which was on the base of all primary sources of a version of the frame, in the consideration of orientation stability for a long time span. Results from examinations show that the coordinates in the N-Cat series catalogues are in consistence, and that the stability of the orientation is better than O.lmas, which is superior to the A-Cat series catalogues as well as the IERS combined catalogues. Some results also show that the orientation of the IERS combined catalogues in 1992 and 1993 did not coincide with each other very well, some attention should be paid for this point.