arXiv subjects

H. Krásná

Publications and source records attributed to H. Krásná.

4 recordsLinked to original sources

arXiv2026

Consistency and precision of very long baseline interferometry source coordinate time series

Coordinate time series of extragalactic radio sources from very long baseline interferometry observations are widely used to evaluate source positional stability, select stable sources for celestial reference frames, assess reference-frame axis stability, and investigate source-related astrometric variability. Their external consistency, realistic errors, and relation to processing strategies and analysis configurations remain to be investigated. We aim to compare coordinate time series solutions from different analysis centers and investigate how processing strategies and configurations contribute to their differences. We collected eight solutions from seven analysis centers and selected 496 common sources after data selection, reference-frame alignment, and extraction of common observing sessions. Inter-solution differences were characterized with pairwise positional offsets and correlation analysis, and realistic positional errors with the N-cornered-hat (NCH) method and bootstrap resampling. Most solutions have median weighted root mean square (WRMS) values of a few hundred microarcseconds $(\mathrm{μas})$, and the median NCH-derived precision is about 200-300 $\mathrm{μas}$ in right ascension and 250-400 $\mathrm{μas}$ in declination. Solutions with similar strategies, software, or source constraints show higher consistency, with more similar WRMS values, stronger correlations, and closer precision estimates. Consistency is affected not only by the global or independent mode distinction but also by detailed analysis configuration. NCH-derived precision depends on declination, being poorer in the southern sky, and stabilizes with more observing sessions. Processing strategies and configurations introduce marginal differences; solutions remain generally consistent. Inter-solution comparisons independently estimate realistic stochastic errors beyond formal errors.

astro-ph.IM↗

arXiv2025

Mitigating Source Structure in Geodetic VLBI on the Visibility Level

Geodetic and astrometric VLBI has entered a new era with the implementation of the VLBI Global Observing System (VGOS). These broadband and dual linear polarization observations aim at an accuracy of station coordinates of 1 mm and a reference frame stability of 0.1 mm/year. Although the extended brightness distribution of many of the radio-loud active galactic nuclei observed during geodetic VLBI sessions is resolved by the interferometer, the established processing chain still treats these objects as point sources. We investigate the impact of source structure on the visibility level and develop tools to remove the structure from the visibility data, right after correlation. Here we present our approach and show results obtained from observational VGOS data.

astro-ph.IM↗

arXiv2022

VLBI Celestial and Terrestrial Reference Frames VIE2022b

Context: We introduce the computation of global reference frames from Very Long Baseline Interferometry (VLBI) observations at the Vienna International VLBI Service for Geodesy and Astrometry (IVS) Analysis Center (VIE) in detail. We focus on the celestial and terrestrial frames from our two latest solutions VIE2020 and VIE2022b. Aims: The current International Celestial and Terrestrial Reference Frames, ICRF3 and ITRF2020, include VLBI observations until spring 2018 and December 2020, respectively. We provide terrestrial and celestial reference frames including VLBI sessions until June 2022 organized by the IVS. Methods: Vienna terrestrial and celestial reference frames are computed in a common least squares adjustment of geodetic and astrometric VLBI observations with the Vienna VLBI and Satellite Software (VieVS). Results: We provide high-quality celestial and terrestrial reference frames computed from 24-hour IVS observing sessions. The CRF provides positions of 5407 radio sources. In particular, positions of sources with few observations at the time of the ICRF3 calculation could be improved. The frame also includes positions of 870 new radio sources, which are not included in ICRF3. The additional observations beyond the data used for ITRF2020 provide a more reliable estimation of positions and linear velocities of newly established VLBI Global Observing System (VGOS) telescopes.

astro-ph.IM↗

arXiv2018

Measurement of the solar system acceleration using the Earth scale factor

We propose an alternative method to detect the secular aberration drift induced by the solar system acceleration due to the attraction to the Galaxy centre. This method is free of the individual radio source proper motion caused by intrinsic structure variation. We developed a procedure to estimate the scale factor directly from very long baseline interferometry (VLBI) data analysis in a source-wise mode within a global solution. The scale factor is estimated for each reference radio source individually as a function of astrometric coordinates (right ascension and declination). This approach splits the systematic dipole effect and uncorrelated motions on the level of observational parameters. We processed VLBI observations from 1979.7 to 2016.5 to obtain the scale factor estimates for more than 4,000 reference radio sources. We show that the estimates highlight a dipole systematics aligned with the direction to the centre of the Galaxy. With this method we obtained a Galactocentric acceleration vector with an amplitude of 5.2 $\pm$ 0.2 μas/yr and direction $α_G = 281°\pm 3°$ and $δ_G = -35°\pm 3°$.

astro-ph.GA↗