Empirical Earth rotation model: a consistent way to evaluate Earth orientation parameters

It is customary to perform analysis of the Earth's rotation in two steps: first, to present results of estimation of the Earth orientation parameters in the form of time series based on a simplified model of variations of the Earth's rotation for a short period of time, and then to process this time series of adjustments by applying smoothing, re-sampling and other numerical algorithms. Although this approach saves computational time, it suffers from self-inconsistency: total Earth orientation parameters depend on a subjective choice of the apriori Earth orientation model, cross-correlations between points of time series are lost, and results of an operational analysis per se have a limited use for end users. An alternative approach of direct estimation of the coefficients of expansion of Euler angle perturbations into basis functions is developed. These coefficients describe the Earth's rotation over entire period of observations and are evaluated simultaneously with station positions, source coordinates and other parameters in a single LSQ solution. In the framework of this approach considerably larger errors in apriori EOP model are tolerated. This approach gives a significant conceptual simplification of representation of the Earth's rotation.Comment: To be published in the Proceedings of the Geodetic Reference Frame symposium held in Muenchen in October 2006. 6 pages, 2 table

The KCAL VERA 22 GHz calibrator survey

We observed at 22 GHz with the VLBI array VERA a sample of 1536 sources with correlated flux densities brighter than 200 mJy at 8 GHz. One half of target sources has been detected. The detection limit was around 200 mJy. We derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths. The objective of these observations was to determine the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies. Preliminary results indicate that the number of compact extragalactic sources at 22 GHz brighter than a given correlated flux density level is twice less than at 8 GHz.Comment: Accepted for publication by the Astronomical Journal. 6 pages, 3 figures, 3 table. The machine readable catalogue file, kcal_cat.txt can be extracted from the source of this submissio

The catalogue of positions of optically bright extragalactic radio sources OBRS-1

It is expected that the European Space Agency mission Gaia will make possible to determine coordinates in the optical domain of more than 500000 quasars. In 2006, a radio astrometry project was launched with the overall goal to make comparison of coordinate systems derived from future space-born astrometry instruments with the coordinate system constructed from analysis of the global very long baseline interferometry (VLBI) more robust. Investigation of their rotation, zonal errors, and the non-alignment of the radio and optical positions caused by both radio and optical structures are important for validation of both techniques. In order to support these studies, the densification of the list of compact extragalactic objects that are bright in both radio and optical ranges is desirable. A set of 105 objects from the list of 398 compact extragalactic radio sources with declination > -10 deg was observed with the VLBA+EVN with the primary goal of producing their images with milliarcsecond resolution. These sources are brighter than 18 magnitude at V band, and they were previously detected at the European VLBI network. In this paper coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these VLBI observations following the method of absolute astrometry. The catalogue of positions of 105 target sources is presented. The accuracies of sources coordinates are in the range of 0.3 to 7 mas, with the median 1.1 mas.Comment: 6 pages, 1 figure, accepted by the Astronomical Journal, ID: AJ-10606. Electronic table 2 with the catalogue is available in the source code of this submissio

On significance of VLBI/Gaia position offsets

We have cross matched the Gaia Data Release 1 secondary dataset that contains positions of 1.14 billion objects against the most complete to date catalogue of VLBI positions of 11.4 thousand sources, almost exclusively active galactic nuclei. We found 6,064 matches, i.e. 53% radio objects. The median uncertainty of VLBI positions is a factor of 4 smaller than the median uncertainties of their optical counterparts. Our analysis shows that the distribution of normalized arc lengths significantly deviates from Rayleigh shape with an excess of objects with small normalized arc lengths and with a number of outliers. We found that 6% matches have radio optical offsets significant at 99% confidence level. Therefore, we conclude there exists a population of objects with genuine offsets between centroids of radio and optical emission.Comment: 6 pages, 6 figures, 3 tables; accepted by MNRAS Letters; full electronic versions of 2 tables are available from the preprint source; text and tables are updated, a figure adde

Precise absolute astrometry from the VLBA imaging and polarimetry survey at 5 GHz

We present in this paper accurate positions of 857 sources derived from the astrometric analysis of 16 eleven-hour experiments from the Very Long Baseline Array imaging and polarimetry survey at 5 GHz (VIPS). Among observed sources, positions of 430 objects were not determined before at a milliarcsecond level of accuracy. For 95% of the sources the uncertainty of their positions range from 0.3 to 0.9 mas, with the median value of 0.5 mas. This estimate of accuracy is substantiated by the comparison of positions of 386 sources that were previously observed in astrometric programs simultaneously at 2.3/8.6 GHz. Surprisingly, the ionosphere contribution to group delay was adequately modeled with the use of the total electron contents maps derived from GPS observations and only marginally affected estimates of source coordinates.Comment: Accepted for publication by the Astronomical Journal. 7 pages, 2 tables, 4 figures. Submission contains an ascii file with the catalogue. You can get the catalogue by downloading the source of this paper and extracting file table2.tx