Comparison with other catalogues.
Before comparing two catalogues all common stars were identified within the uncertainty radius of 3 arcsec. No rejection of identified pairs using statistical criteria (like 3 sigma etc.) was fulfiled.
To analise the dependence of differences on magnitude we divided the whole magnitude range into sub-bands (bins) with 0.5 mag or 0.25 mag sizes. In each bin average values of dra*cos(dec), dmura*cos(dec), ddec, dmudec and their rms deviations as well as the mean magnitude of stars belonging to this bin were calculated.
To find out the behavior of position and proper motion differences depending on the location in the sky stars within a narrow magnitude range (1-2 mag sized) were selected then for these stars mean differences were calculated.
Move to:
When considering the dependence of position and proper motion differences on magnitude it became clear that their mean values do not exceed 10 mas for positions at J2000 and 1 mas/yr for proper motions, and their rms deviations depend on magnitude and change from 50 to 120 mas for positions and from 3 to 7 mas/yr for proper motions.
As for differences in individual fields it found out that starting from about 13 mag the coordinat-depended systematic differences between XC1 and UCAC2 proper motions appear. The differences dmura (ra) and dmudec (ra) have a wave-like behavior with 360-degree period and in the range of magnitudes from 13 to 15 mag they have amplitudes 0.8 mas/yr and 1.4 mas/yr respectively. Moreover in differences dmudec (dec) a slope beginning from about 40 degree declinations is observed.
 |
 |
 |
 |
 |
 |
 |
 |
The differences between XC1 and KMAC1T proper motions were calculated at J2000 epoch. Their mean values do not exceed 10 mas in declinations but reach 40 mas in right ascentions around 16 mag (see figure). Rms deviations of the differences range from 70 mas in the bright part to 500 mas around 17 mag. >
 |
 |
 |
 |
Before calculating differences between XC1 and 2MASS positions each star of the XC1 catalogue was shifted using proper motions to the 2MASS observation epoch. Mean values of these differences do not exceed 10 mas in both coordinates. Their rms deviations increase smoothly from 60 mas in the bright part to 90 mas around 16 mag then from 16.5 mag climb up sharply. >
 |
 |
As is well known the USNOB1 proper motions were received with respect to stars having magnitudes from 18 to 20 which were considered as relatively motionless. But the XC1 catalogue system is refered to ICRS/Tycho2 one. Therefore the presence of systematic position and proper motion differences
Standart deviations of position and proper motion differences are comparable large: about 150 mas in positions and 4.5 mas/yr in proper motions and remain nearly constant in the magnitud range from 13 to 18.
There are also systematic differences between XC1 and USNOB1 proper motions depending on the location in the sky on a large scale up to 10 mas/yr which .
 |
 |
 |
 |
 |
 |