CATALOGUES OF INTERMEDIATE STARS IN RADIO SOURCES VICINITIES.

Kumkova I., Kolomietz A.

IAA RAS, 8 Zhdanovskaya str., St.Petersburg, 197042 RUSSIA

One of the most important task of modern astrometry is extension of radio coordinate reference frame adopted as new IAU reference frame to the optical catalogues, namely FK5 and Hipparcos one. The accurate positions of extragalactic radio sources (ERS) can be used to link the radio and fundamental reference frame and to contribute to determining relative orientation of Hipparcos and the radio reference frames as well as Hipparcos one and FK5. The optical positions of radio source counterparts are obtained by means of photographic astrometry. Due to difference in stellar magnitude between the ERS and catalogue stars of the FK5 and HIPPARCOS reference frame, a multistep method of positional determination is applied . In this method two systems of intermediate stars in vicinities of ERS are used: the first system of intermediate stars of 6-9 stellar magnitude, whose positions are given in reference catalogues, and the second system of intermediate stars of 12-14 stellar magnitude, whose positions must be obtained in process of work. Catalogues of intermediate stars chosen in ERS vicinities is a very important part of link between radio and optical frames via compact extragalactic radio sources as the positional accuracy and configuration of stars influence on the accuracy of obtained parameters. In framework of different programs aimed to establishing a link between radio and optical reference frames and carrying out in observatories over the world, the different catalogues of intermediate stars have been used. For example, in program CONFOR we catalogues of intermediate stars were compiled. Mostly the catalogues has as a basis the same list of ERS. Different authors use the own criteria of selection of intermediate stars, so despite the same centers of areas the catalogues differ. The existing catalogues of intermediate stars using in different programs are considered.The description of main catalogues is given. Results of investigation and comparison of 5 catalogues of intermediate stars from ERS vicinities are presented.