External accuracy estimation using extragalactic objects.
Among stars of the XC1 catalogue 126 optical components of ICRF sources, several thousands galaxies from Lion Extragalactic Database as well as several thousands quasars from various lists mainly from SDSS Quasar Catalog III (DR3 Quasars) and "Quasars and Active Galactic Nuclei" (Veron+, 2003) were identified within uncertainty radius of 3 arcsec. All objects inside of this circle, without exception, were considered as common ones. Since there are positions and formal proper motions for these objects the external estimation of random and systematic accuracy of XC1 can be found.
Move to:- Positions of ICRF sources.
- Formal proper motions of ICRF sources.
- Formal proper motions of LEDA galaxies.
- Formal proper motions of DR3 quasars.
- Back
Positions of ICRF sources.
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Mean values of position differences are +10.0 and +1.8 mas
for RA and DEC respectively.
Std. deviations are 135 and 100 mas for RA and DEC respectively.
As can be seen from figures sited above there is no dependence of position differences between XC1 and ICRF catalogues on the magnitude or the field location on the sky. The discrepancy between the average values of the position difference for RA and DEC as well as their rms deviations can be explained by the presence of large individual deviations. The average values of these differenes are near zero.
Formal proper motions of ICRF sources.
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Mean values of proper motions are -0.17 and -0.27 mas/yr
for muRA and muDEC respectively.
Std. deviations are 2.5 and 2.7 mas/yr for muRA and muDEC respectively.
The diagrams sited above show the dependences of the formal proper motions on the magnitude and the location on the sky. It is clear that their average values are near zero. Rms deviations of the formal proper motions in right ascensions and declinations are 2.5 mas/yr and 2.7 mas/yr respectively; this characterize the accuracy of proper motions of stars. This estimation is in quite good agreement with the formal internal error of proper motions in the range of magnitudes from 17 to 18.
Formal proper motions of LEDA galaxies.
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Mean values of proper motions are +0.03 and -0.08 mas/yr
for muRA and muDEC respectively.
Std. deviations are 4.1 and 3.9 mas/yr for muRA and muDEC respectively.
There is no dependence of the proper motions on the magnitude as well as on the location on the sky. The small differences in rms deviations apparently can be explained by worth accuracy of measurements of exteded objects.
Formal proper motions of DR3 quasars.
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Mean values of proper motions are -0.20 and -0.28 mas/yr
for muRA and muDEC respectively.
Std. deviations are 3.5 and 3.2 mas/yr for muRA and muDEC respectively.
The absence of points on individual pieces of graphs can be explained by the specific distribution of DR3 quasars over the sky. Otherwise behaviors of proper motions of DR3, ICRF quasars and LEDA galaxies are quite similar.