On comparison and combination of catalogues of radio source positions

Free access article

Issue		A&A Volume 474, Number 2, November I 2007


Page(s)		665 - 670
Section		Celestial mechanics and astrometry
DOI		http://dx.doi.org/10.1051/0004-6361:20077450

A&A 474, 665-670 (2007)
DOI: 10.1051/0004-6361:20077450

On comparison and combination of catalogues of radio source positions

Ju. Sokolova and Z. Malkin

Central Astronomical Observatory at Pulkovo RAS, Pulkovskoe Ch. 65/1, St. Petersburg 196140, Russia
e-mail: s0lei@yandex.ru

(Received 10 March 2007 / Accepted 18 August 2007)

Abstract
Context.Radio source catalogues (RSCs) obtained from very long baseline interferometry (VLBI) observations are recommended by the International Astronomical Union (IAU) as realizations of the International Celestial Reference Frame (ICRF). As the accuracy of the VLBI observations is improving with time, development of more accurate methods of RSC construction is a topical problem.
Aims.In this paper we search for an optimal method of representation of the RSC systematic errors and investigate a possibility for improving the ICRF by means of combining individual RSCs.
Methods.Four methods of representing the RSC systematic differences have been examined by comparison of the differences in the radio source positions between the individual catalogues. Eight radio source catalogues and the latest ICRF realization, ICRF-Ext.2, were used for comparison. After selection of the best method of difference representation we computed the systematic differences between each individual catalogue and the ICRF. These differences were then used in the construction of the combined radio source catalogue.
Results.Representation of the systematic differences between RSCs with the Legendre-Fourier functions proved to be the most accurate method. Using this method, two combined radio source catalogues have been constructed. The first of them provides a stochastic improvement of the current realization of ICRF, and the second, final one allows us to account also for possible systematic errors in the ICRF. Comparison of the celestial pole offsets obtained from the processing of VLBI observations using ICRF and the combined catalogue has shown improvement of the results.
Conclusions.The conventional method of individual radio source catalogue comparisons used by the International Earth Rotation and Reference Systems Service does not provide sufficient accuracy and should be replaced by a more adequate method. A combined radio source catalogue allows us to improve the current realization of the ICRF.

Key words: astrometry -- reference systems -- techniques: interferometric -- ephemerides

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.