Institute of Astronomy > Laboratory of astrometry > Fields of research > Creating high presize catalogues of positions and proper motions of stars > XC1 catalogue
XC1 is the catalogue of positions and proper motions of stars in the ICRS/Tycho2 system; it was created in the laboratory of astrometry of the Research institute of Astronomy of the V. N. Karazin Kharkiv National University. This catalogue contains equatorial coordinates and proper motions of stars in the magnitude range from 10 to 20 in one square degree fields around about 350 ICRF sources in the northern sky.
For creating this catalogue Schmidt plates of Palomar surveys POSS-1 and POSS-2 digitized by means PMM machine were used. For each one square degree field of the sky we had at least 5 plates, taken in different filters. There are two sets of observations which relate to different time periods: the fist epoch is between 1949 and 1954 years, and the second one - between 1980 and 1990 years. The catalog presented below is the preliminary release of the final one, howbeit it represent all original features.
In the current version of the catalogue proper motions were derived using positions of stars, which were present at least in 5 plates (two plates of the first epoch and three plates of the second one), and positions of stars from 2MASS catalogue when it was possible. In deriving positions and proper motions of stars we used 5-10 individual positions of catalogue objects obtained in various epochs. To eliminate the magnitude equation approximate magnitudes were derived. For this purpose the catalogue USNO-B1 were adopted, its magnitides were used as reference ones. Colour equation was not taken in account. We are going to eliminate it in the next catalogue version.
The main goal of creating XC1 catalogue was to extend Tycho2 system to fainter magnitudes with maximal accuracy which can be achieved. The solution of this problem is nontrivial for several reasons including the presense of significant distorsions on photographic plates and the need to extrapolate the magnitude equation. Nontheless we hope that our internal accuracy estimates are close to real values but we know exactly that there are significant systematic errors in some fields. These errors are caused by magnitude and colour equations as well as by using the PMM digitizing machine.
The external accuracy of positions and proper motions of XC1 catalogue was estimated from its comparison with different current star catalogues. Another way we used is found on the analisis of formal proper motions of galaxies and quasars indentified among "stars" of the XC1.
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