(1) Space Telescope Science Institute.
3700 San Martin Drive, Baltimore, MD 21218, U.S.A.
(2) Astronomical Observatory of Kyiv Taras Shevchenko University.
3 Observatorna street, UA-254053 Kyiv, Ukraine
Due to earth-based nature of traditional astrometric observations there are at least tree regions of the sky which require special attention. First of them is the equatorial zone, second - near-zenith region, and last - the polar regions, northern and southern. In the first two cases the problem is not so dramatic due to averaging the results obtained in many observatories over the world. In the last cases the mentioned canot help us because different condition of observations of stars in low declination zones on the one hand and in high declination zones, on the other hand. Coordinate system singularity produces additional problems when one deals with routine methods of approximation of systematic differences in process of system-to-system transitions. As a result the regions mentioned contains specific errors and requires the special consideration in each case, especially when obtaining the precise positions and proper motions of near-pole stars using observation catalogues produced during essential time span. The main objectives of this work are as follows: (1) to collect and to study the complete observation material of appropriated quality produced during one and a half century; (2) to construct high quality combined catalogues of the positions and proper motions of stars in the regions of 10-degree radius around the poles; (3) to study the accidental and systematic errors of modern catalogues like the PPM and ACRS in the polar region; (4) to apply modern methods for catalog-to-catalog transitions. To achieve the goal thirteen source catalogs, both meridian and photographic, covered an epoch span near one and a half century were collected. The observations carried out in Ukraine (Kyiv, 1880; Kharkiv, 1991,1964, 1984) and other catalogues which were not integrated into the PPM and ACRS will be used additionally. The combined catalogue of positions and proper motions of 4272 stars, northern of 80 degree declination represents the FK5 system, J2000.0. The new catalogue was constructed using the method of infinitely overlapping circles. Overall external rms accuracy of positions for the epoch of 2000 is equal to 0.15 arcsec and 0.25 arcsec for centennial proper motions respectively. The internal rms errors of positions at the mean catalogue epoch (about 1940) are equal to 0.18 and 0.15 arcsec for right ascension and declination correspondingly, while external rms position errors for that epoch is of the order of 0.05 arcsec. The comparison was made between the new catalogue and three modern catalogues, the FK5, PPM, and ACRS. The systematic differences between the new catalogues and the PPM one for the epoch of 2000 are rather valuable. The essential part of systematic differences authors consider as that caused by the PPM shortcomings in the polar zone. For the mean epoch of the new catalogue positions systematic differences are essentially smaller. The large differences were found between PPM and ACRS. Author consider the reason of these discrepances.
Key words: astrometry, FK5-system, position catalogues.