Compared CRF

 

In 2002, three individual celestial frames obtained from VLBI analysis and a compiled one had been submitted to the IERS for their validation. The four frames had been analysed and compared to the ICRF-Ext.1.

 

Analyzed reference frames

[RSC (BKGI) 02 R 01]: This VLBI global combined solution was computed by the BKG VLBI Analysis Centre in cooperation with the VLBI group at the University of Bonn.

[RSC (GAOUA) 01 C 01]: This frame has been elaborated at the Main Astronomical Observatory of the National Academy of Sciences of Ukraine.

[RSC (IAA) 02 R 03]: This celestial frame has been elaborated by the VLBI research group of the IAA Laboratory of New Methods in Astrometry and Geodynamics (NMAG) in Saint Petersburg.

[RSC (GSFC) 02 R 01]: This VLBI solution has been elaborated at the Goddard Space Flight Centre, it has been constrained to be aligned to ICRF-Ext.1.

 

Comparison of individual celestial frames to ICRF-Ext.1

The algorithm of comparison is the one currently used at the ICRS Centre; the coordinate difference between two frames is modelled by a global rotation of the axes, represented by the three angles A1, A2, A3, and by a deformation represented by three parameters: two slopes (Da) and (Dd), and one bias (Bd). Table 1 gives the global orientation between axes of the individual catalogues and those of the ICRS. Table 2 shows the systematic effects in the individual frames detected by their comparison to ICRF-Ext.1.

 
Frame of
N
A1
A2
A3
ra
rd
BKGI
209
+0.036±0.016
+0.004±0.016
-0.053±0.021
0.17
0.23
GAOUA
211
-0.003±0.016
-0.020±0.016
-0.022±0.021
0.17
0.22
IAA
85
-0.009±0.024
+0.018±0.025
-0.023±0.036
0.15
0.23
GSFC
202
+0.000±0.018
-0.023±0.017
-0.044±0.023
0.18
0.24

Tab. 1. A1, A2, A3 are the small angles which transform coordinates from the individual frames into ICRF; N is the number of the common defining ICRF sources used for the comparison; ra and rd are the weighted mean residuals in acos(d) and d respectively. Unit: 0.001".

 
Frame of
Da
Dd
Bd
BKGI
-0.001±0.001
+0.000±0.000
+0.002±0.017
GAOUA
-0.001±0.001
+0.000±0.000
+0.014±0.017
IAA
+0.001±0.001
-0.001±0.001
-0.005±0.038
GSFC
-0.001±0.001
+0.000±0.000
+0.028±0.018

Tab. 2. Da, Dd are the slopes in right ascension and in declination, respectively. Bd is the bias in declination. Units: 0.001"/degree for the slopes, 0.001" for the bias.