arXiv subjects

Zinovy Malkin

Publications and source records attributed to Zinovy Malkin.

At least 19 recordsLinked to original sources

arXiv2026

Simple approximations of some statistical functions

Possibilities are considered to simplify the computation of several statistical functions used to test statistical hypotheses when processing observations: the inverse normal distribution, the Student's t-distribution, and the criterion for rejecting outliers. For these three cases, simple approximation expressions are proposed for the quantiles of these statistical distributions, which are accurate enough for most practical applications.

astro-ph.IM↗

arXiv2025

Evolution of the radio source position uncertainties in radio astrometric catalogs over the past three decades

In this paper, progress in improving the coordinates uncertainty of extragalactic radio sources derived from astrometric and geodetic VLBI observations is investigated. For this purpose, 30 catalogs of radio source positions computed in 1997-2025 were analyzed. Over these years, the median source position uncertainty represented by the semi-major axis of the error ellipse for 467 sources in common to all catalogs improved by one order of magnitude: from 0.156 mas to 0.015 mas. It was also found that the improvement in the position uncertainty over time follows a power law with high accuracy. The number of observations used for determination of the coordinates of the common sources in the input catalogs increased over time from 1.3 to 14.4 million, also following a power law. A discussion of the results led us to the conclusion that the number of observations is the primary factor in improving the source positions uncertainty compared to the number of sessions in which the source was observed.

astro-ph.IM↗

arXiv2025

Preliminary analysis of the annual component of the polar motion over 180-year data interval

The paper presents preliminary results of studying variations in the annual component in the Earth's polar motion. For this purpose, a signal with an annual period was extracted, firstly, from the series of pole coordinates of the International Earth Rotation and Reference Systems Service (IERS), and secondly, from the combined series of Pulkovo latitude variations for 1840--2017. For this purpose, one-dimensional and multidimensional singular spectrum analysis was used. The Hilbert transform was used to calculate the change in the amplitude and phase of the annual oscillation over time. As a result, it turned out that over an interval of about 180 years, an almost monotonic increase in the amplitude of the annual oscillation from $\approx$60~mas to $\approx$90~mas and an almost monotonic phase shift of $\approx$45$^\circ$ are observed. A correlation was also found between the amplitude of the annual component and the difference in average temperatures from November to March in the northern and southern hemispheres.

physics.geo-ph↗

arXiv2025

Should We Expect Further Acceleration of the Earth's Rotation in the Coming Years?

Recently, it has been suggested in the literature that the difference between universal and coordinated time UT1-UTC could reach a large positive value in the coming years (Agnew 2024). This would make it necessary to introduce a negative leap second into UTC for the first time in history, which in turn will cause serious problems in time keeping and synchronization systems around the world. Based on the latest Earth's rotation and universal time data published by the international Earth rotation and reference systems service (IERS) and their prediction, in this paper, we have shown that the acceleration trend observed over the past four years is likely to return to slowing down soon. Therefore, fears about the possible need to introduce a negative leap second into the UTC time scale in the next few years in the light of recent observational data have seen unfounded.

astro-ph.EP↗

arXiv2025

Filling the gap in the IERS C01 polar motion series in 1858.9-1860.9

The C01 Earth orientation parameters (EOP) series provided by the International Earth Rotation and Reference Systems Service (IERS) is the longest reliable record of the Earth's rotation. In particular, the polar motion (PM) series beginning from 1846 provides a basis for investigation of the long-term PM variations. However, the pole coordinate $Y_p$ in the IERS C01 PM series has a 2-year gap, which makes this series not completely evenly spaced. This paper presents the results of the first attempt to overcome this problem and discusses some ways to fill this gap. Two novel approaches were considered for this purpose: parametric astronomical model consisting of the bias and the Chandler and annual wobbles with linearly changing amplitudes, and data-driven model based on Singular Spectrum Analysis (SSA). Both methods were tested with various options to ensure robust and reliable results. The results obtained by the two methods generally agree within the $Y_p$ errors in the IERS C01 series, but the results obtained by the SSA approach can be considered preferable because it is based on a more complete PM model.

physics.geo-ph↗

arXiv2025

Improving source positions in the OCARS catalog: A first approach

OCARS (Optical Characteristics of Astrometric Radio Sources) is a compiled catalog of various additional data associated with astrometric radio sources whose coordinates have been determined from very long baseline interferometry (VLBI) observations. It contains source coordinates, object type, redshift, optical and near-infrared magnitudes. Until now, OCARS source coordinates were simply copied from input catalogs and, as a result, were systematically inhomogeneous. This work is the first attempt to obtain a unified set of radio source coordinates aligned to the International Celestial Reference Frame (ICRF), more specically to the third ICRF release, ICRF3. Comparison of the source coordinates in the old OCARS version as of December 2024 and the new OCARS version as of March 2025 with the ICRF3-SX catalog using the vector spherical harmonics (VSH) technique showed almost complete elimination of systematic errors in new OCARS positions relative to the ICRF3 frame.

astro-ph.IM↗

arXiv2024

On the Use of Vector Spherical Harmonics

In many astronomical works, the structure of vector fields is analyzed, such as the differences in the celestial object coordinates in catalogs or the celestial object velocities, by decomposition into vector spherical harmonics (VSH). This method has shown high efficiency in many studies, but, at the same time, comparing the results obtained by different authors can cause difficulties associated with different approaches to building the VSH system and even with their different designations. To facilitate this task, this paper provides a comparison of the three VSH systems most often used in works on astrometry and stellar astronomy.

astro-ph.IM↗

arXiv2023

On the most reliable value of the Galactic aberration constant

Galactic aberration (GA) is a small effect in proper motions of celestial objects with an amplitude of about 5 $μ$as/yr already noticeable in highly accurate astrometric observations such as VLBI and Gaia. However accurate accounting for this effect faces difficulty caused by the uncertainty in the GA amplitude (GA constant). Its estimates derived from VLBI and Gaia data processing differ significantly, so it would be very desirable to involve another independent method to solve the problem of inconsistency between these two methods. Such a method, that we consider in this paper, is using determination of the Galactic rotation parameters by methods of stellar astronomy. The result obtained in this study showed that the GA constant estimate obtained from stellar astronomy is closer to the estimate obtained from Gaia.

astro-ph.IM↗

arXiv2021

Statistical analysis of the results of 20 years of activity of the International VLBI Service for Geodesy and Astrometry

2019 marked the 20th anniversary of the International VLBI Service for Geodesy and Astrometry (IVS). This service is the largest and most authoritative organization that coordinates international activities in radio astrometry and VLBI sub-system of space geodesy. Currently, about 60 antennas located in many countries on all continents participate in the IVS observing programs. The IVS Data Centers have accumulated more than 18 million observations obtained during more than 17'000 sessions, including more than 10,000 Intensive sessions for rapid determination of Universal Time. The paper traces the dynamics of IVS development based on statistical processing of the array of observations collected in the IVS Data Centers for the period of 1979-2018. Various statistics by the years, stations, baselines, and radio sources are provided. The evolution of the IVS observational data and the accuracy of results obtained from processing VLBI observations is considered.

astro-ph.IM↗

arXiv2021

Towards a robust estimation of orientation parameters between ICRF and $Gaia$ celestial reference frames

An analysis of the source position differences between VLBI-based ICRF and $Gaia$-CRF catalogues is a key step in assessing their systematic errors and determining their mutual orientation. One of the main factors that limits the accuracy of determination of the orientation parameters between two frames is the impact of outliers. To mitigate this effect, a new method is proposed based on pixelization data over the equal-area cells, followed by median filtering of the data in each cell. After this, a new data set is formed, consisting of data points near-uniformly distributed over the sphere. The vector spherical harmonics (VSH) decomposition is then applied to this data to finally compute the orientation parameters between ICRF and $Gaia$ frames. To validate the proposed approach, a comparison was made of the ICRF3-SX and $Gaia$~DR2 catalogues using several methods for outliers removal. The results of this work showed that the proposed method is practically insensitive to outliers and thus provides much more robust results of catalogues comparison than the methods used so far. This conclusion was confirmed by analogous test comparison of the $Gaia$~DR2 and OCARS catalogues.

astro-ph.IM↗

arXiv2021

On the selection of prospective sources for ICRF extension

Despite continuous increasing of the number of ICRF sources, their sky coverage is still not satisfactory. The goal of this study is to discuss some new considerations for extending the ICRF source list. Statistical analysis of the ICRF catalog allows us to identify less populated sky regions where new ICRF sources or additional observations of the current ICRF sources are most desirable to improve both the uniformity of the source distribution and the uniformity of the distribution of the position errors. It is also desirable to include more sources with high redshift in the ICRF list. These sources may be of interest for astrophysics. To select prospective new ICRF sources, the OCARS catalog is used. The number of sources in OCARS is about three times greater than in the ICRF3, which gives us an opportunity to select new ICRF sources that have already be tested and detected in astrometric and geodetic VLBI experiments.

astro-ph.IM↗

arXiv2021

Comparison of ground-based and Gaia photometry of astrometric radio sources

A comparison was made between $Gaia$ magnitudes and magnitudes obtained from ground-based observations for astrometric radio sources . The comparison showed that these magnitudes often not agree well. There may be several reasons for this disagreement. Nevertheless, such an analysis can serve as an additional filter for verification of the object cross-identification. On the other hand, it can help to detect possible errors in optical magnitudes of astrometric radio sources coming from unreliable or inconsistent data sources.

astro-ph.IM↗

arXiv2019

Spherical Rectangular Equal-Area Grid (SREAG): Some features

A new method Spherical Rectangular Equal-Area Grid (SREAG) was proposed in Malkin (2019) for splitting spherical surface into equal-area rectangular cells. In this work, some more detailed features of SREAG are presented. The maximum number of rings that can be achieved with SREAG for coding with 32-bit integer is $N_{ring}$=41068, which corresponds to the finest resolution of $\sim$16$''$. Computational precision of the SREAG is tested. The worst level of precision is $7\cdot10^{-12}$ for large $N_{ring}$. Simple expressions were derived to calculate the number of rings for the desired number of cells and for the required resolution.

astro-ph.IM↗

arXiv2019

Outstanding Pulkovo latitude observers Lidia Kostina and Natalia Persiyaninova

Lidia Dmitrievna Kostina and Natalia Romanovna Persiyaninova left a bright mark in the history of the Pulkovo Observatory, as well as in the history of the domestic and international latitude services. In the first place, they were absolute leaders in the latitude observations with the famous zenith telescope ZTF-135. In 1954-2001, they obtained together more than 66'000 highly accurate latitudes, which make about 2/3 of all the observations made by 23 observers with the ZTF-135 after the WW2. They also provided a large contribution to investigation of the instrumental errors, methods of the data analysis, developing of the observing programs. Their results in studies of the latitude variations and polar motion were also highly recognized by the community.

astro-ph.IM↗

arXiv2019

A new equal-area isolatitudinal grid on a spherical surface

A new method SREAG (spherical rectangular equal-area grid) is proposed to divide a spherical surface into equal-area cells. The method is based on dividing a sphere into latitudinal rings of near-constant width with further splitting each ring into equal-area cells. It is simple in construction and use, and provides more uniform width of the latitudinal rings than other methods of equal-area pixelization of a spherical surface. The new method provides a rectangular grid cells with the latitude- and longitude-oriented boundaries, near-square cells in the equatorial rings, and the closest to uniform width of the latitudinal rings as compared with other equal-area isolatitudinal grids. The binned data is easy to visualize and interpret in terms of the longitude-latitude rectangular coordinate system, natural for astronomy and geodesy. Grids with arbitrary number of rings and, consequently, wide and theoretically unlimited range of cell size can be built by the proposed method. Comparison with other methods used in astronomical research showed the advantages of the new approach in sense of uniformity of the ring width, a wider range of grid resolution, and simplicity of use.

astro-ph.IM↗

arXiv2018

A new version of the OCARS catalog of Optical Characteristics of Astrometric Radio Sources

A new version of the Optical Characteristics of Astrometric Radio Sources (OCARS) catalog is presented. This compiled catalog includes radio sources observed in different VLBI programs and experiments that result in source position determination, their redshift, and photometry in the visible and near-infrared bands. A cross-identification table between the OCARS and other catalogs is also provided. The status of the catalog as of 2018 September 7 is described in this paper. The OCARS catalog currently contains 6432 sources, of which 3895 have redshift data and 5479 have photometric data. Compared with the previous version, the current version has been enriched with extended redshift and photometry information, and cross-identification with several catalogs in radio, optical, infrared, ultraviolet, X-ray, and gamma-ray bands. The OCARS catalog is updated every few weeks on average to incorporate new data that appear in the NASA/IPAC Extragalactic Database (NED), SIMBAD database, and in the literature.

astro-ph.IM↗

arXiv2018

Toward reinforcing the link between Gaia and ICRF frames

The link problem between radio (VLBI/ICRF) and optical (Gaia/GCRF) celestial reference frames is analyzed. Both systems should be a realization of the ICRS (International Celestial Reference System) at microarcsecond level of accuracy. Therefore, the link between the ICRF and GCRF should be obtained with similar accuracy, which is not a trivial task due to relatively large systematic and random errors in source positions at different frequency bands. In this presentation, additional possibilities to improve the GCRF-ICRF link accuracy are discussed. In particular, a possibility to increase the number of ICRF and GCRF common objects is considered using advanced scheduling of the regular IVS sessions such as R1 and R4. It is shown that inclusion of supplement prospective southern sources in these sessions allows enriching southern ICRF zone without noticeable loss of accuracy of geodetic results. Another topic discussed in this presentation is using the correlations between radio source coordinates, which can impact the orientation angles between two frames at a level of a few tens of microarcseconds.

astro-ph.IM↗

arXiv2017

A new method to subdivide a spherical surface into equal-area cells

A new method is proposed to divide a spherical surface into equal-area cells. The method is based on dividing a sphere into several latitudinal bands of near-constant span with further division of each band into equal-area cells. It is simple in construction and provides more uniform latitude step be-tween latitudinal bands than other methods of isolatitudinal equal-area tessellation of a spherical surface.

astro-ph.IM↗