On comparison and combination of catalogues of radio source positions

Sokolova, Julia; Malkin, Zinovy

doi:10.1051/0004-6361:20077450

Cited by 22 publications

(18 citation statements)

References 7 publications

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“…They were submitted by JPL (Caltech/NASA Jet Propulsion Laboratory, USA), and USNO (US Naval Observatory, USA). A brief description of the input catalogs is given in Table 1 ( Sokolova & Malkin 2007). This section is divided into two subsections.…”

Section: Using Two Different Quasar Catalogs To Improve the Icrf-ext2mentioning

confidence: 99%

“…Different methods were used to obtain a combined RSC with (Arias et al 1988) being the first of them, and others were proposed by Walter (1989aWalter ( , 1989b and Yatskiv (1990). In accordance with Sokolova (2007), appropriate use of individual catalogs with common sources provides an improvement of each individual catalog. Among the general aims regarding this subject, we can point out the comparative study between catalogs and ICRF defining sources by considering a rigid frame (only rotations), avoiding deformations, and considering the densification of the ICRF in a twofold sense: the increased amount of defining sources and the densification in its wider sense of the catalog.…”

Section: Introductionmentioning

confidence: 99%

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Homogenization in compiling ICRF combined catalogs

Marco

Martínez

López

2013

A&A

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Context. The International Astronomical Union (IAU) recommendations regarding the International Celestial Reference Frame (ICRF) realizations require the construction of radio sources catalogs obtained using very-long-baseline interferometry (VLBI) methods. The improvement of these catalogs is a necessary procedure for the further densification of the ICRF over the celestial sphere. Aims. The different positions obtained from several catalogs using common sources to the ICRF make it necessary to critically revise the different methods employed in improving the ICRF from several radio sources catalogs. In this sense, a revision of the analytical and the statistical methods is necessary in line with their advantages and disadvantages. We have a double goal: first, we propose an adequate treatment of the residual of several catalogs to obtain a homogeneous catalog; second, we attempt to discern whether a combined catalog is homogeneous. Methods. We define homogeneity as applied to our problem in a dual sense: the first deals with the spatial distribution of the data over the celestial sphere. The second has a statistical meaning, as we consider that homogeneity exists when the residual between a given catalog and the ICRF behaves as a unimodal pure Gaussian. We use a nonparametrical method, which enables us to homogeneously extend the statistical properties of the residual over the entire sphere. This intermediate adjustment allows for subsequent computation of the coefficients for any parametrical adjustment model that has a higher accuracy and greater stability, and it prevents problems related with direct adjustments using the models. On the other hand, the homogeneity of the residuals in a catalog is tested using different weights. Our procedure also serves to propose the most suitable weights to maintain homogeneity in the final results. We perform a test using the ICRF-Ext2, JPL, and USNO quasar catalogs. Results. We show that a combination of catalogs can only be homogeneous if we configure the weights carefully. In addition, we provide a procedure to detect inhomogeneities, which could introduce deformities, in these combined catalogs.Conclusions. An inappropriate use of analytical adjustment methods provides erroneous results. Analogously, it is not possible to obtain homogeneous-combined catalogs unless we use the adequate weights.

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Section: Using Two Different Quasar Catalogs To Improve the Icrf-ext2mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Homogenization in compiling ICRF combined catalogs

Marco

Martínez

López

2013

A&A

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“…Studies comparing radio source catalogues have found that ad-hoc methods which systematically shift source declinations by different amounts depending on declination are effective in improving the agreement between different catalogues (Arias & Bouquillon 2004;Sokolova & Malkin 2007), and it is possible this is partly an effect of a declination degeneracy.…”

Section: Comparing Cataloguesmentioning

confidence: 99%

The declination degeneracy in interferometric astrometry

Buscher

2012

A&A

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Context. Interferometric astrometry at radio and optical wavelengths serves as a fundamental and high-precision method for measuring the positions of celestial objects and for geodetic and Earth orientation measurements. Aims. We determine the importance and form of the degeneracy which arises when the interferometric baselines and the celestial target positions are estimated simultaneously from the same data under circumstances where the declination range of the targets is limited. Methods. Heuristic analyses of an idealised interferometric experiment were used to determine how a degeneracy could arise as a result of limited declination coverage and what form it might take. Singular Value Decomposition of simulated experiments with different declination coverages and different hour-angle coverages were then used to quantify the level of degeneracy present and the form of the degeneracy in example cases. Results. A significant degeneracy was found which depends strongly on the declination coverage and less strongly on the hour-angle coverage of the experiment. The degeneracy is significant even when the declination coverage extends from the pole to the equator. The degeneracy takes the form of a systematic distortion of the measured coordinates in the declination direction which is larger near the equator than at the poles, together with a corresponding baseline distortion. Conclusions. Taking into account this degeneracy in a quantitative way can have a significant effect on the design and interpretation of astrometric and geodetic experiments.

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“…Other interesting transformations based on Legendre-Fourier functions have been developed by Sokolova & Malkin (2007) to model differences between catalogues of several hundreds of sources. Here, we only keep degree 1 and 2 describing translations and rotations, respectively.…”

Section: Generation Of Source Coordinate Time Seriesmentioning

confidence: 99%

On radio source selection to define a stable celestial frame

Lambert

Gontier

2008

A&A

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Context. The most accurate realization of a quasi inertial reference frame, the International Celestial Reference Frame (ICRF), is made of 212 defining extragalactic radio sources whose coordinates are determined using VLBI observations. Recent studies demonstrated however that using other sets of sources could improve the frame stability. Aims. This study examines a simple radio source selection scheme to define celestial reference frame axes more stable than the ones as currently defined by the ICRF. Methods. After having derived source coordinate time series from 26 years of VLBI observations, we select the most suitable sources on the basis of their positional variability (rms and slope), and observational history. We determine the axis stability of the frame defined by the selection, as well as its suitability for global geodetic VLBI analyses, i.e., determination of Earth orientation parameters and source and station coordinates. Results. We select four frames made of 196, 200, 262, and 269 sources, respectively, showing a satisfactory sky coverage in both hemispheres. Our selections provide a frame stability improved by up to 40% with respect to the ICRF, and by 20% with respect to the frame as defined by the 247 stable sources of Feissel-Vernier et al. (2006, A&A, 452, 1107). Reanalysis of data with respect to this frame gives astrometric catalogues aligned to the ICRF-Ext.2 within 17 μas. Effects on the Earth orientation parameter estimates and terrestrial reference frame determination remain marginal. Conclusions. In view of the generation of the next ICRF, we recommend that such an algorithm be taken into consideration along with other criteria based on individual characteristics of the radio sources.

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On comparison and combination of catalogues of radio source positions

Cited by 22 publications

References 7 publications

Homogenization in compiling ICRF combined catalogs

Homogenization in compiling ICRF combined catalogs

The declination degeneracy in interferometric astrometry

On radio source selection to define a stable celestial frame

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