Combined astrometric catalogue EOC-3 *
An improved reference frame for long-term Earth rotation studies
Astronomical Institute, Academy of Sciences of Czech Republic, Boční II, 141 31 Prague 4, Czech Republic e-mail: [vondrak;stefka]@ig.cas.cz
Accepted: 13 October 2006
Context.In the past, we collected the astrometric observations of latitude/universal time variations made worldwide at 33 observatories. These observations, re-analyzed with the Hipparcos Catalogue, were then used to determine the Earth Orientation Parameters (EOP) at 5-day intervals, covering the interval 1899.7–1992.0. Later on, new astrometric catalogues (such as ARHIP or TYCHO-2) appeared as combination of Hipparcos/Tycho positions with ground-based catalogues. These catalogues yield more accurate proper motions than the original Hipparcos Catalogue.
Aims.Many of the objects observed in the programmes of monitoring Earth orientation from the ground are double or multiple systems, having non-negligible periodic motions. We aim at obtaining a star catalogue with improved proper motions and quasi-periodic terms reflecting orbital motions of the stars observed in these programmes.
Methods.We used about 4.5 million observations of latitude/universal time variations, and combined them with the catalogues ARIHIP, TYCHO-2, etc. to obtain a new Earth Orientation Catalogue (EOC). These are the same ground-based observations that were used to construct the previous version, EOC-2. Spectral analysis of ground-based data is performed to discover which of the observed objects display periodic motion, and the method of least squares is then used to estimate corresponding amplitudes and phases.
Results.The third version of the catalogue, EOC-3, contains 4418 different objects (i.e., stars, components of double stars, photocenters). Our attempt leads to a description of more accurate paths of the observed objects that will be eventually used for another determination of the Earth Orientation Parameters in the twentieth century.
Key words: reference systems / astrometry / catalogs
© ESO, 2007