arXiv subjects

V. V. Bobylev

Publications and source records attributed to V. V. Bobylev.

At least 19 recordsLinked to original sources

arXiv2026

Search for a Globular Cluster whose Passage through the Galactic Disk could Trigger the Radcliffe Wave

Using a catalog of 152 globular clusters (GCs), their orbits were constructed to determine their intersections with the Galaxy's plane of symmetry. Young open star clusters (OSCs) were selected from the selection zone characteristic of the Radcliffe wave. The Hunt and Reffert catalog served as the source of data on these OSCs. A grouping of 17 OSCs with an average age of 32.7 million years was found. It is compact in coordinate, velocity, and age space. This grouping is shown to be a good candidate for the hypothesis that the Radcliffe wave is generated by the passage of an impactor through the Galaxy's plane of symmetry, with the impactor being the GC NGC~4372. The last time it crossed the galactic plane was 55.5 million years ago, and 22.2 million years later, a burst of star formation occurred at this location, forming a whole group of open-clustered stars, and possibly the Radcliffe wave as a whole.

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arXiv2026

The Radcliffe Wave is not alone in the Local System

The spatial distribution of open star clusters (OSCs) younger than 30 million years old in the Local System was studied. It was shown for the first time that a significant number of OSCs belong to the recently discovered Vela Ridge gas and dust supercloud. The most intriguing property of this sample of OSCs is the presence of periodic perturbations in their vertical coordinates with a maximum amplitude of 47 pc and a wavelength of 1.1 kpc. Thus, the discovered chain of young OSCs is analogous to the Radcliffe Wave, but with a lower amplitude of vertical perturbations, a shorter wavelength, and is, on average, 2 million years older.

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arXiv2026

Features of the distribution of absorbing matter in the local system

V. I. Sorokina$^1$\footnote [99]{e-mail: vasilisushka05@gmail.com}, V. V. Bobylev$^2$, G. A. Gontcharov$^{2}$, A. T. Bajkova$^2$A detailed study of the dust distribution in the Local System was conducted. Using the latest map by Gontcharov et al., smoothed distributions of dust matter were obtained in projection onto the galactic plane $XY$ using various smoothing parameters. Within the 2-kpc radius region around the Sun under study, key structural features associated with the Radcliffe Wave, Split, Sagittarius Spur Extension, Malpolon+Natrix, and Vela Ridge superclouds are clearly identified. It was shown that the Radcliffe Wave, Malpolon+Natrix, and Vela Ridge regions exhibit periodic perturbations of vertical coordinates with wavelengths ranging from 2.5 kpc (Radcliffe Wave) to 2 kpc (Malpolon+Natrix and Vela Ridge). No similar long-wavelength, high-amplitude oscillations of vertical coordinates were detected in the Sagittarius Spur Extension and Split regions.

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arXiv2026

Three Models of the Gravitational Potential of the Milky Way

The parameters of an axisymmetric model for the gravitational potential of the Galaxy have been refined. The basic curve of the Galaxy's rotation in a distance interval of $R:0-190$ kpc was constructed using the velocities of masers, classical Cepheids, Red Clump stars, Blue Horizontal Branch stars, halo stars, globular clusters, and dwarf satellite galaxies of the Milky Way. The rotation curve was selected in such a way that there would be no dominant burst of circular velocities in the central ($R<2$ kpc) region of the Galaxy. As a result, we constructed two two-component models of the galactic potential, which include contributions from the disk and the halo of invisible matter, as well as a three-component model with a small-mass bulge added in advance. These models can be useful in studying the long-term orbital evolution of stars and open and globular star clusters in the central ($R<4$ kpc) region of the Galaxy. The constructed models were tested for self-consistency by comparing their rotation curves with a set of model curves generated with the Illustris TNG50 software package.

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arXiv2025

Analysis of Orbital Dynamics of Globular Clusters in the Central Region of the Milky Way

The regularity/chaoticity of orbits of 45 globular clusters in the central region of the Galaxy with a radius of 3.5 kpc, which are subject to the greatest influence of the elongated rotating bar, is analyzed. Various methods of analysis are used, namely, the methods of calculating the maximum characteristic Lyapunov exponents (MCLE), MEGNO (Mean Exponential Growth factor of Nearby Orbits), the Poincaré section method, the frequency method based on calculating fundamental frequencies, and a new method is proposed based on calculating the orbit amplitude spectrum as a function of time and calculating the entropy of the amplitude spectrum as a measure of orbital chaos. Bimodality is found in the histogram of the distribution of positive Lyapunov exponents calculated in the classical version, without renormalizing the shadow orbit, which allows implementing a probabilistic method for GC classification, which is also a new approach. To construct the orbits of globular clusters, we used the gravitational potential model with a bar in the form of a triaxial ellipsoid. The following bar parameters were adopted: mass $10^{10} M_\odot$, length of the semi-major axis 5 kpc, angle of rotation of the bar axis 25$^o$, rotation velocity 40 km s$^{-1}$ kpc$^{-1}$. To form the 6D-phase space required for integrating the orbits, we used the most accurate astrometric data to date from the Gaia satellite (EDR3), as well as new refined average distances to globular clusters. Globular clusters with regular and chaotic dynamics were classified.

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arXiv2025

Age Estimation of the Radcliffe Wave from Open Star Clusters

Four samples of open star clusters (OSCs) with average ages of 5.2, 18.6, 40, and 61 Myr have been analyzed. The selection of these OSCs was carried out from a narrow region inclined to the galactic axis y at an angle of 25$^\circ$. The spectral analysis of the vertical positions and velocities of the selected clusters showed that the Radcliffe wave is associated with OSCs no older than 30 Myr. The following estimates of the Radcliffe wave characteristics were obtained for the OSCs with an average age of 5.2 Myr: $z_{max}=117\pm12$ pc with the wavelength $λ=4.55\pm0.14$ kpc, the vertical velocity disturbance amplitude $W_{max}=4.86\pm0.19$ km s$^{-1}$ with the wavelength $λ=1.74\pm0.08$ kpc. For the OSCs with an average age of 18.6 Myr, the estimates are as follows: $z_{max} = 54\pm5$ pc and $λ=6.30\pm0.12$ kpc, the vertical velocity disturbance amplitude $W_{max}=7.90\pm0.16$ km s$^{-1}$ and $λ=0.83\pm0.11$ kpc. The radial motion of the Radcliffe wave away from the galactic center has been confirmed. The velocity of such movement is 10 pc Myr$^{-1}$. In our opinion, the spatial distribution of OSCs younger than 30 Myr does not contradict the hypothesis of the association of the Radcliffe wave with the impact of shock waves from supernova explosions that arose on an extended front comparable in scale to the entire wave, that is, about 2 kpc in size.

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arXiv2023

The Influence of the Bar on the Dynamics of Globular Clusters in the Central Region of the Milky Way. Frequency Analysis of Orbits According to Gaia EDR3 Data

This work is devoted to studying the influence of the bar on the orbital dynamics of globular clusters. The orbits of 45 globular clusters in the central galactic region with a radius of 3.5 kpc were analyzed using spectral dynamics methods in order to identify objects captured by the bar. To form the 6D phase space required for orbit integration, the most accurate astrometric data to date from the Gaia satellite (EDR3), as well as new refined average distances to globular clusters, were used. Since the parameters of the Milky Way bar are known with very great uncertainty, the orbits were constructed and their frequency analysis was carried out with varying the mass, length and angular velocity of rotation of the bar in a wide range of values with a fairly small step. The integration of orbits was carried out at 2.5 billion years ago. As a result, bar-supporting globular clusters were identified for each set of bar parameters. For the first time, an analytical expression has been obtained for the dependence of the dominant frequency $f_X$ on the angular velocity of rotation of the bar. In addition, the probabilities of capturing globular clusters by the bar were determined when the bar parameters were varied in certain ranges of values according to a random distribution law. A list of 14 globular clusters with the most significant capture probabilities is given, with five GCs - NGC6266, NGC6569, Terzan 5, NGC6522, NGC6540 - showing the probability capture by bar $\geq 0.2$. A conclusion is made about the regularity of the orbits of globular clusters based on the calculation of approximations of the maximum characteristic Lyapunov exponents.

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arXiv2023

Globular clusters in the central region of the Milky Way galaxy I. Bar influence on the orbit parameters according to Gaia EDR3

The work is devoted to the analysis of the influence of the galactic bar on the orbital motion of globular clusters in the central region of the Galaxy. For this task, 45 globular clusters were selected, 34 of which belong to the bulge/bar and 11 to the disk. The most accurate astrometric data from the Gaia satellite (Vasiliev and Baumgardt, 2021), as well as new refined average distances (Baumgardt and Vasiliev, 2021), were used to form the 6D-phase space required for orbit integration. The orbits of globular clusters are obtained both in an axisymmetric potential and in a potential including a bar. In this case, the mass, rotation velocity, shape and scale length of the bar were varied. A comparison is made of such orbital parameters as apocentric and pericentric distances, eccentricity and maximum distance from the galactic plane. It is shown that the mass of the bar exerts the greatest influence on the orbital motion, which is expressed mainly in an increase in both the apocentric and pericentric distances in the vast majority of globular clusters. The eccentricities of the orbits in the overwhelming majority also change significantly, and there is a change both upward and downward, especially in the range of values from 0.2 to 0.8. The greatest changes in parameters are observed in globular clusters with high radial velocities and small pericentric distances. The change in orbital parameters depending on the bar rotation velocity is less pronounced. The influence of the geometric parameters of the bar is insignificant in the accepted range of their changes. Several examples show that globular clusters in the bulge are more affected by the bar than those belonging to the disk.

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arXiv2023

Review of current estimates of the Galaxy mass

An overview of the methods used to estimate the mass of the Galaxy and the results obtained by various authors recently according to modern data is given. In particular, the estimates obtained based on the analysis of the galactic rotation curve, on the kinematics of the Galactic dwarf satellites and globular clusters, on the streams of such dwarf galaxies, on escape speed, as well as on halo stars are considered. Estimates of the Galaxy mass in the form $M (<r)$, $M_{\rm 200}$ and $M_{\rm vir}$ are considered. According to 20 individual estimates, the average value was found $\overline M_{\rm 200}=0.88\times 10^{12}~M_\odot$ with a dispersion of $0.24\times 10^{12}~M_\odot$ and a weighted average error of $0.06\times 10^{12}~M_\odot$. According to 25 individual estimates, $\overline M_{\rm vir}=1.02\times10^{12}~M_\odot$ was obtained with a dispersion of $0.41\times 10^{12}~M_\odot$ and a weighted average error of $0.09\times10^{12}~M_\odot$.

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arXiv2023

Rotation Curve and Mass Distribution in the Galaxy from the Velocities of Objects at Distances up to 200 kpc

Three three-component (bulge, disk, halo) model Galactic gravitational potentials differing by the expression for the dark matter halo are considered. The central (bulge) and disk components are described by the Miyamoto-Nagai expressions. The Allen-Santill'an (I), Wilkinson-Evans (II), and Navarro-Frenk-White (III) models are used to describe the halo. A set of present-day observational data in the range of Galactocentric distances R from 0 to 200 kpc is used to refine the parameters of these models. The model rotation curves have been fitted to the observed velocities by taking into account the constraints on the local matter density ρ_\odotand the force K_{z=1.1} acting perpendicularly to the Galactic plane. The Galactic mass within a sphere of radius 50 kpc, M_G (R<=50 kpc)=(0.41+/-0.12)x10^12 M_\odot, is shown to satisfy all three models. The differences between the models become increasingly significant with increasing radius R. In model I, the Galactic mass within a sphere of radius 200 kpc turns out to be greatest among the models considered, M_G (R<=200 kpc)=(1.45+/-0.30)x10^12 M_\odot, and the smallest value has been found in model II, M_G (R<=200 kpc)=(0.61+/-0.12)x10^{12} M_\odot. In our view, model III is the best one among those considered, because it ensures the smallest residual between the data and the constructed model rotation curve provided that the constraints on the local parameters hold with a high accuracy. Here, the Galactic mass is M_G (R<=200 kpc)=(0.75+/-0.19)x10^12 M_\odot. A comparative analysis with the models by Irrgang et al. (2013), including those using the integration of orbits for the two globular clusters NGC 104 and NGC 1851 as an example, has been performed. The third model is shown to have subjected to a significant improvement.

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arXiv2023

A New Catalog of orbits of 152 Globular Clusters from Gaia EDR3

This paper provides a new catalog of orbits and their parameters for a practically complete list of currently known galactic globular clusters (GCs), compiled by Vasiliev (2019) based on the most accurate modern measurements of their velocities and positions. The integration of the orbits of 152 globular clusters for 5 Gyr backward was performed using the new average proper motions obtained from the Gaia EDR3 catalog (Vasiliev and Baumgardt, 2021) and new average distances (Baumgardt and Vasiliev, 2021) in the axisymmetric three-component potential with spherical bulge, disk component, and spherical dark Navarro-Frank-White halo (Bajkova and Bobylev, 2016). The new orbital parameters are compared with the orbital parameters constructed by us earlier (Bajkova and Bobylev, 2021) in the same gravitational potential using proper motions obtained from the Gaia DR2 catalog (Vasiliev, 2019) and with the distances from the Harris catalog (2010).

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arXiv2023

Kinematics of the Galaxy from Cepheids with proper motions from the Gaia DR1 catalogue

The sample of classic Cepheids with known distances and line-of-sight velocities is supplemented by the proper motions from the Gaia DR1 catalog. From spatial velocities of 260 stars the components of the peculiar Solar velocity: (U,V,W)_\odot=(7.90,11.73,7.39)+/-(0.65,0.77,0.62) km/s, parameters of the Galactic rotation curve: Ω_0 =28.840+/-.33 km/s/kpc, Ω'_0=-4.05+/-0.10 km/s/kpc^2, Ω''_0=0.805+/-0.067 km/s/kpc^3 are obtained. For the adopted Galactocentric Solar distance R_0=8 kpc the linear circular velocity of the Local Standard of Rest is found as V_0=231+/-6 km/s.

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arXiv2023

3-D kinematics of classical Cepheids according to Gaia, EDR3 catalog

The kinematics of about 2000 classical Cepheids of the Milky Way with data from Gaia\,EDR3 catalog has been studied. For some of these stars, there are line-of-sight velocities. On the basis of the nonlinear rotation model, the parameters of the rotation curve of the Galaxy were determined. The circular linear rotation velocity of the near-solar neighborhood around the Galaxy center was $V_0=236\pm 3$~km s$^{-1}$ for the assumed Sun's galactocentric distance $R_0=8.1\pm0.1$~kpc. Analysis of residual velocities of Cepheids based on the linear Ogorodnikov-Milne model showed the presence of the following significantly different from zero gradients: $\partial U/\partial x,$ $\partial U/\partial z,$ $\partial V/\partial x,$ $\partial V/\partial z$ and $\partial W/\partial x,$ which behaves differently depending on the selection radius. The most interesting is the gradient $\partial W/\partial x\sim-0.5\pm0.1$~km s$^{-1}$ kpc$^{-1}$ (positive rotation of this star system around the galactic axis $y$, $Ω_y$) since the velocities $W$ are free of galactic rotation. Here we have an indirect influence of various effects leading to a perturbation of the vertical velocities of the galactic disk stars. Based on a simpler model, a more accurate estimate of this rotation is obtained, $Ω_y=0.51\pm0.07$~km s$^{-1}$ kpc$^{-1}$.

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arXiv2022

Study of the structure and kinematics of the Galaxy according to VLBI astrometry of masers and radio stars

In recent years, radio interferometric observations have achieved high accuracy in determining the absolute values of trigonometric parallaxes and proper motions of maser radiation sources and radio stars. The error in determining the trigonometric parallaxes of these objects averages about 10 microarcseconds, which allows us to confidently study the geometric and kinematic properties of the distribution of stars located at great distances from the Sun, up to the center of the Galaxy. This article provides an overview of the main results of studying the structure and kinematics of the Galaxy, which were obtained by various scientific teams using VLBI observations of masers and radio stars. The main attention is paid to the results of studying the Galaxy obtained by the authors of this work.

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arXiv2022

The Mysterious Radcliffe Wave

The review is devoted to the Radcliffe Wave recently discovered by Alves et al. from the analysis of molecular clouds. These authors singled out a narrow chain of molecular clouds, elongated almost in one line, located at an inclination of about 30$^o$ to the galactic axis y. The Radcliffe Wave itself describes damped vertical oscillations of molecular clouds with a maximum oscillation amplitude of about 160 pc and a characteristic wavelength of about 2.5 kpc. To date, the presence of the Radcliffe Wave has been confirmed in the vertical distribution of a) interstellar dust, b) sources of maser radiation and radio stars, which are very young stars and protostars closely associated with molecular clouds, c) low-mass stars of the T Tau type, d) more massive OB stars and e) young open clusters of stars. The Radcliffe Wave is also traced in the vertical velocities of young stars. Most of the considered results of the analysis of the vertical velocities of various young stars show that the oscillations of the vertical positions and vertical velocities of stars in the Radcliffe Wave occur synchronously. The nature of the Radcliffe Wave is completely unclear. The majority of researchers associate its occurrence with the assumption of an external gravitational impact on the galactic disk of a striker such as a dwarf satellite galaxy of the Milky Way.

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arXiv2022

Three-Dimensional Kinematics of Classical Cepheids

A linear Ogorodnikov-Milne model is applied to study the three-dimensional kinematics of classical Cepheids in the Milky Way. A sample of 832 classical Cepheids from Mr'oz et al. (2019) with distances, line-of-sight velocities, and proper motions from the Gaia DR2 catalogue is used. The Cepheid space velocities have been freed from the differential Galactic rotation found by us previously based on a nonlinear rotation model. Based on a complete Ogorodnikov-Milne model, involving the line-of-sight velocities and proper motions of stars, we have estimated the angular velocity of rotation around the Galactic $y$ axis, $Ω_y=0.64\pm0.17$~km s$^{-1}$ kpc$^{-1}$. We think that this rotation is associated with the warp of the Galactic thin disk. Our calculations using only the proper motions of Cepheids under the assumption of no deformations due to the disk warp have shown the presence of a residual rotation around the $y$ axis with an angular velocity $Ω_y=0.54\pm0.15$~km s$^{-1}$ kpc$^{-1}$ and the presence of a positive rotation around the $x$ axis with an angular velocity $Ω_x=0.33\pm0.10$~km s$^{-1}$ kpc$^{-1}$.

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arXiv2022

Analysis of the Distance Scales by Cepheids from the Gaia EDR3 Catalogue Data

We study the kinematics of a sample of classical Cepheids younger than 120 Myr. For these stars, the estimates of distances taken from Skowron et al., which are based on the period-luminosity relation, and the line-of-sight velocities and the proper motions from the Gaia catalog are available. There are also distance estimates derived from the trigonometric parallaxes contained in the Gaia ERD3 catalog. A method, which relies on comparison of the first-order derivative of the Galactic rotation angular velocity, showed the need to lengthen the distance scales determined by Skowron et al. by about 10%. This conclusion was confirmed by direct comparison to the distances predicted on using the trigonometric parallaxes. With taking into account this result, we obtained new estimates of the Galactic rotation parameters and the parameters of a spiral density wave.

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arXiv2022

Estimation of Galactic Spiral Density Wave Parameters Based on the Velocities of OB2 stars from the Gaia EDR3 Catalogue

We have analyzed the kinematics of 9750 OB2 stars with proper motions and parallaxes selected by Xu et al. from the Gaia EDR3 catalogue. The relative parallax errors for these stars do not exceed 10\%. Based on the entire sample of stars, we have found the velocities $(U,V)_\odot=(7.17,7.37)\pm(0.16,0.24)$ km s$^{-1}$ and the components of the angular velocity of Galactic rotation: $Ω_0 =29.700\pm0.076$ km s$^{-1}$ kpc$^{-1}$, $Ω^{'}_0 =-4.008\pm0.022$ km s$^{-1}$ kpc$^{-2}$, and $Ω^{''}_0 = 0.671\pm0.011$ km s$^{-1}$ kpc$^{-3}$, where the linear rotation velocity of the Galaxy at the solar distance is $V_0=240.6\pm3.0$ km s$^{-1}$ for the adopted $R_0=8.1\pm0.1$ kpc. There are 1812 OB2 stars with measured line-of-sight velocities, and the space velocities $V_R$ and $ΔV_{circ}$ have been calculated from them. Based on a spectral analysis independently for the radial and residual tangential velocities, we have obtained the following estimates: $f_R=4.8\pm0.7$ km s$^{-1}$, $f_θ=4.1\pm0.9$ km s$^{-1}$, $λ_R=2.1\pm0.2$ kpc, $λ_θ=2.2\pm0.4$ kpc, $(χ_\odot)_R=-116\pm12^\circ$, and $(χ_\odot)_θ=-156\pm14^\circ$ for the adopted four-armed ($m = 4$) spiral pattern. Thus, both velocity perturbation amplitudes are nonzero at a high significance level.

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