arXiv subjects

Vadim Bobylev

Publications and source records attributed to Vadim Bobylev.

At least 19 recordsLinked to original sources

arXiv2026

Search for galactic structures and study of their kinematics in the Gaia era

The characteristics of Gaia catalogues, such as trigonometric parallaxes and proper motions of stars, are discussed. Radial velocities of stars are also important for studying spatial motions. The most important results of the kinematics analysis of stellar groups from the nearest vicinity of the Sun are noted, where Gaia data allow estimating a number of parameters with unprecedentedly high accuracy. The issues related to the rotation of the Galaxy and its spiral structure are touched upon. The properties of the Radcliffe wave are discussed in the light of new data. An answer is obtained to the question of the existence of an analogue of the Radcliffe wave in other places of the Galaxy. The discovery of a phase spiral in the $z-V_z$ plane, made using Gaia data, is noted.

astro-ph.GA↗

arXiv2026

Comparison of Static and Evolving Potentials in the Orbital Dynamics of Globular Clusters in the Central Region of the Galaxy

A comparative analysis of the dynamics of the orbital motion (regular or chaotic) of 45 globular clusters in the central region of the Galaxy with a radius of 3.5 kpc is carried out. The static and evolving (based on the semi-analytical cosmological model of Gomez et al. (2010) and Hagi et al. (2015)) potentials of the Galaxy are considered both in the form of an axisymmetric and non-axisymmetric potential of the Galaxy with a rotating elongated bar with the following parameters at the present time: mass $10^{10} M_\odot$, length of the major semi-axis 5 kpc, rotation angle of the bar axis 25$^o$, angular velocity of rotation 40 km s$^{-1}$ kpc$^{-1}$ . To form the 6D-phase space required for integrating the orbits, the most accurate astrometric data to date from the Gaia satellite (Vasiliev \& Baumgardt, 2021), as well as new refined average distances (Baumgardt \& Vasiliev, 2021) were used. We used a frequency method for analysis of the chaotic/regular orbital motion of all 45 GCs. The results are summarized in the table, which provides an overview of each GC in our sample, the degree of chaotization in both the static and evolving potentials, and the influence of the central rotating bar on the degree of orbital chaotization in both cases. It is shown that the orbital dynamics have undergone minor changes during the transition from the static to the evolving potential. This confirms our previously obtained result that changes in the masses and sizes of the gravitational potential components act on orbital parameters in opposite ways, and at small galactocentric distances this influence is maximally compensated, while the orbits of distant objects and objects with large apocentric distances experience the greatest influence.

astro-ph.GA↗

arXiv2025

Relationship between Poincar\'e Sections and Spectral Characteristics of Orbits of Globular Clusters in the Central Region of the Galaxy

In the paper, orbital dynamics, regular or chaotic, of globular clusters (GCs) in the central region of the Galaxy, which is subject to the greatest influence of the rotating bar, has been studied. Such methods for determining chaos as Poincar\'e sections and spectral methods have been compared. The relationship between the Poincar\'e sections and the spectral characteristics of the orbits has been estimated. The sample includes 45 globular clusters in the central region of the Galaxy with a radius of 3.5 kpc. To form the 6D-phase space required for integrating the orbits, the most accurate astrometric data to date from the Gaia satellite, as well as new refined average distances, have been used. The following, most realistic, bar parameters have been adopted: mass $10^{10} M_\odot$, length of the major semi-axis of the bar model in the form of a triaxial ellipsoid is 5 kpc, angle of rotation of the bar axis is $25^o$, rotation velocity is 40 km s$^{-1}$ kpc $^{-1}$. The result of the study is that a 100\% correlation between the classification by Poincar\'e sections and the spectral characteristics of the orbits has been established. Consequently, the classification by Poincar\'e sections can be replaced by a more visual analysis of the amplitude spectra of the orbits. Thus, two lists of GCs: with regular and chaotic dynamics have been compiled. The GCs with varying degrees of orbital chaos have separately been distinguish.

astro-ph.GA↗

arXiv2025

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

A new method for determining the nature of the orbital motion (chaotic or regular) of globular clusters in the central region of the Galaxy with a radius of 3.5 kpc, which are most affected by the bar, is proposed. The method is based on calculating the orbital power spectrum as a function of time and calculating the entropy of the power spectrum as a measure of orbital chaos. The sample includes 45 globular clusters. To form the 6D phase space required for integrating the orbits, the most accurate astrometric data to date from the Gaia satellite (Vasiliev \& Baumgardt, 2021) were used, as well as new refined average distances (Baumgardt \& Vasiliev, 2021). Orbits of globular clusters are obtained in a non-axisymmetric potential with a bar in the form of a triaxial ellipsoid embedded in an axisymmetric potential, traditionally used by us to construct orbits of globular clusters, described in detail in the paper by Bajkova et al. (2023a). The following, most realistic, bar parameters are adopted: mass $10^{10} M_\odot$, length of the major semi-axis 5 kpc, angle of rotation of the bar axis 25$^o$, angular velocity of rotation 40 km s$^{-1}$ kpc$^{-1}$. A list of 23 globular clusters with regular dynamics and 22 globular clusters with chaotic dynamics is determined. The correlation of the obtained classification of globular clusters with the classification obtained by us using other methods in the work of Bajkova et al. (2024a) was determined.

astro-ph.GA↗

arXiv2024

The influence of the bar on the chaotic dynamics of globular clusters in the central region of the Galaxy

The paper is devoted to the analysis of the influence of the galactic bar on the nature of the orbital motion (chaotic or regular) of 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 bar. The sample includes 45 globular clusters. To form the 6D phase space required for integrating the orbits, the most accurate astrometric data to date from the Gaia satellite (Vasiliev, Baumgardt, 2021) were used, as well as new refined average distances (Baumgardt, Vasiliev, 2021). The orbits of the globular clusters were obtained both in an axisymmetric potential and in a potential including the bar. The following, most realistic, bar parameters were adopted: mass $10^{10} M_\odot$, semi-major axis length 5 kpc, bar axis rotation angle 25$^o$, angular rotation velocity 40 km s$^{-1}$ kpc$^{-1}$. The analysis of the chaoticity/regularity of the orbital motion in both potentials was carried out using one of the most effective methods, namely, the frequency method, which consists in calculating the drift of fundamental frequencies. As a result, the influence of the bar on the dynamics of each GC of the sample was assessed. It is established that 8 GCs changed regular dynamics to chaotic under the influence of the bar, and 9 GCs changed chaotic dynamics to regular one.

astro-ph.GA↗

arXiv2024

Analysis of regularity/chaoticity of the globular clusters dynamics on the central region of the Milky Way

We analyzed the regularity/chaoticity of the 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 from an elongated rotating bar. Various analysis methods were used, namely, methods for calculating the Highest Lyapunov Exponents, the method of Poincar$\acute{e}$ sections, the frequency method based on the calculation of fundamental frequencies, as well as the visual assessment method. Bimodality was discovered in the histogram of the distribution of positive Lyapunov exponents, calculated in the classical version, without renormalization of the shadow orbit, which makes it possible to implement a probabilistic method of GC classification. To construct the orbits of globular clusters, we used a gravitational potential model with a bar in the form of a triaxial ellipsoid, described in detail in the work of Bajkova et al., Izvestiya Glavnoi astronomicheskoi observatorii v Pulkove, {\bf 228}, 1 (2023). The following bar parameters were adopted: mass $10^{10} M_\odot $, semimajor axis length 5 kpc, bar viewing angle 25$^o$, rotation velocity 40 km s$^{-1}$ kpc$^{-1}$. To form the 6D-phase space required for orbit integration, the most accurate astrometric data to date from the Gaia satellite (EDR3) (Vasiliev, Baumgardt, 2021), as well as new refined average distances to globular clusters (Baumgardt, Vasiliev, 2021) were used. A classification is made of globular clusters with regular and chaotic dynamics. As the analysis showed, globular clusters with small pericentric distances and large eccentricities are most susceptible to the influence of the bar and demonstrate the greatest chaos. It is shown that the results of classifying globular clusters by the nature of their orbital dynamics, obtained using the various methods of analysis considered in the work, correlate well with each other.

astro-ph.GA↗

arXiv2024

Estimates of the kinematic age of the $β$ Pictoris moving group from up-to-date data

The kinematics of about 40 single stars belonging to the $β$ Pictoris moving group is studied. The age of the $β$ Pictoris moving group is estimated from these stars with ground-based line-of-sight velocity determinations by two methods. Both estimates are kinematic. In the first method we considered the traceback trajectories of the stars, giving an estimate of $t=13.2\pm1.4$ Myr. In the second method, by analyzing the instantaneous velocities of the stars, we show that there is an expansion of the stellar system occurring in the Galactic $xy$ plane. Based on this effect, we find the time interval elapsed from the beginning of the expansion of the $β$ Pictoris moving group to the present day, $t=20\pm2$ Myr.

astro-ph.GA↗

arXiv2023

Search for Close Stellar Encounters with the Solar System Based on Data from the Gaia DR3 Catalogue

A search for close encounters of stars with the Solar System was performed using data from the Gaia\,DR3 catalog. We considered 31 stars with the approach parameter $d_{\rm min}<1$~pc. Among them, 15 stars are appearing as candidates for close encounters for the first time. The status of the stars GJ\,710 and HD\,7977 has been confirmed as candidates for deep penetration into the inner region of the Oort cloud. In particular, for GJ\,710 and HD\,7977, respectively, the following estimates of approach parameters are obtained: $t_{\rm min}= 1.324\pm0.026$~Myr and $d_{\rm min}=0.052\pm0.002$~pc, $t_{\rm min}=-2.830\pm0.025$~Myr and $d_{\rm min}=0.071\pm0.027$~pc. Among the newly identified candidates, the most interesting is the white dwarf WD\,0810-353, for which the following approach parameters were found: $t_{\rm min}=0.029\pm0.001$~Myr and $d_{\rm min}=0.150\pm0.003$~pc.

astro-ph.GA↗

arXiv2023

Redetermination of the Parameters of the Galactic Spiral Pattern from Classical Cepheids

We have studied a sample of Galactic classical Cepheids with their distance estimates taken from Skowron et al. (2019), where they were determined based on the period-luminosity relation. In this paper the Skowron et al. (2019) distances were increased by 10\%, according to the results of our kinematic analysis of these Cepheids obtained by us previously. We have refined the geometric characteristics of two spiral arms: the Carina-Sagittarius and Outer ones. The Galactocentric distance of the Sun was assumed to be $8.1\pm0.1$~kpc. Based on 257 Cepheids belonging to a Carina-Sagittarius arm segment with ages in the range 80--120 Myr, we have found the pitch angle of the spiral pattern $i=-12.7\pm0.4^\circ$ and the position of this arm $a_0=7.28\pm0.05$~kpc. Based on 352 Cepheids from the Outer arm with ages in the range 120--300 Myr, we have found $i=-12.0\pm0.5^\circ$ and $a_0=13.03\pm0.06$~kpc. Based on a sample of 1618 Cepheids with ages in the range 80--300 Myr, we have constructed a wavelet map in the ``position angle--logarithm of distance'' plane. The following estimates have been obtained from our analysis of this map: $i=-12.9\pm0.4^\circ$ and $a_0=7.43\pm0.05$~kpc for the Carina-Sagittarius arm and $i=-12.5\pm0 .5^\circ$ and $a_0=13.33\pm0.06$~kpc for the Outer arm. We have found that the Sun is very close to the corotation radius that is located between the Sun and the Perseus arm and estimates the angular rotation speed of the spiral pattern $Ω_p = 27\pm1$ km s$^{-1}$ kpc$^{-1}$.

astro-ph.GA↗

arXiv2022

Parameters of the Galactic Spiral Density Wave from Masers with Parallax Errors Less Than 10%

We have studied the kinematics of Galactic masers and radio stars with measured VLBI trigonometric parallaxes and proper motions. We have considered masers with relative trigonometric parallax errors less than 10\% and determined the Galactic rotation parameters from them. In particular, the linear rotation velocity of the Galaxy at the solar distance $R_0$ has been found to be $244.4\pm4.3$ km s$^{-1}$ (for the adopted $R_0=8.1\pm0.1$ kpc). We have performed a joint and separate spectral analysis of the radial, residual tangential, and vertical maser velocities. For example, from the vertical maser velocities we have estimated the velocity perturbation amplitude $f_W=5.2\pm1.5$ km s$^{-1}$ with the wavelength $λ_W=2.6\pm0.7$ kpc, arguing for the influence of the spiral density wave on the vertical stellar velocities. Based on 104 masers within 3 kpc of the Sun, as a result of the joint solution, we have estimated the radial, $f_R=6.7\pm1.1$ km s$^{-1}$, and tangential, $f_θ=2.6\pm1.2$ km s$^{-1}$, velocity perturbations, the perturbation wavelength $λ=2.1\pm0.3$ kpc, and the Sun's phase in the Galactic spiral density wave $χ_\odot=-148\pm15^\circ$. We have confirmed the presence of the Radcliffe wave in the spatial distribution of masers and radio stars belonging to the Local Arm.

astro-ph.GA↗

arXiv2022

Parameters of the Radcliffe wave from masers, radio stars and T Tauri stars

The presence of the Radcliffe wave is shown both in the positions and in the vertical velocities of masers and radio stars belonging to the Local Arm. This gives the impression that the structure of the Radcliffe wave is not a wave in the full sense of the word. It is more like a local high-amplitude burst, rapidly fading away. Moreover, this structure has the largest amplitude in the immediate vicinity of the Sun, where the main ``contributors'' are the Gould Belt stars. Based on the spectral analysis of masers, the following estimates of the geometric and kinematic characteristics of the wave were obtained: the largest value of the vertical coordinate $z_{max}=87\pm4$ pc and the wavelength $λ=2.8\pm0.1$ kpc, the vertical velocity perturbation amplitude reaches $W_{max}=5.1\pm0.7$ km s$^{-1}$ and the wavelength found from vertical velocities is $λ=3.9\pm1.6$ kpc. The Radcliffe wave also manifests itself in the positions of very young stars that have not reached the main sequence stage. We extracted a sample of such stars from the Gaia DR2$\times$AllWISE database and obtained the following estimates from them: $z_{max}=118\pm3$ pc and wavelength $λ=2.0\pm0.1$ kpc.

astro-ph.GA↗

arXiv2018

Refinement of Parameters of Six Selected Galactic Potential Models

This paper is devoted to the refinement of the parameters of the six three-component (bulge, disk, halo) axisymmetric Galactic gravitational potential models on the basis of modern data on circular velocities of Galactic objects located at distances up to 200 kpc from the Galactic center. In all models the bulge and disk are described by the Miyamoto--Nagai expressions. To describe the halo, the models of Allen-Santillán (I), Wilkinson-Evans (II), Navarro-Frenk-White (III), Binney (IV), Plummer (V), and Hernquist (VI) are used. The sought-for parameters of potential models are determined by fitting the model rotation curves to the measured velocities, taking into account restrictions on the local dynamical matter density $ρ_\odot=0.1 M_\odot$ pc$^{-3}$ and the vertical force $|K_{z=1.1}|/2πG=77 M_\odot $ pc$^{-2}$. A comparative analysis of the refined potential models is made and for each of the models the estimates of a number of the Galactic characteristics are presented.

astro-ph.GA↗

arXiv2017

Search for Close Stellar Encounters with the Solar System from Data on Nearby Dwarfs

Trigonometric parallaxes measured with ground-based telescopes of the RECONS consortium as part of the CTIOPI program are used to search for stars that have either had an encounter with the solar system in the past or will have such an encounter in the future, at distances of less than a few parsecs. These are mainly low-mass dwarfs and subdwarfs of types M, L, and T currently at distances of less than 30 pc from the Sun. Six stars for which encounters with the solar orbit at distances of less than 1 pc are possible have been identified for the first time. For example, the minimum distance for the star **SOZ 3A will 0.72+/- 0.11 pc at an epoch of 103+/-44 thousand years in the future.

astro-ph.GA↗

arXiv2014

The local standard of rest from data on young objects with account for the Galactic spiral density wave

To estimate the peculiar velocity of the Sun with respect to the Local Standard of Rest (LSR), we used young objects in the Solar neighborhood with distance measurement errors within 10%-15%. These objects were the nearest Hipparcos stars of spectral classes O-B2.5, masers with trigonometric parallaxes measured by means of VLBI, and two samples of the youngest and middle-aged Cepheids. The most significant component of motion of all these stars is induced by the spiral density wave. As a result of using all these samples and taking into account the differential Galactic rotation, as well as the influence of the spiral density wave, we obtained the following components of the vector of the peculiar velocity of the Sun with respect to the LSR: (Uo,Vo,Wo)_{LSR}=(6.0,10.6,6.5)+\-(0.5,0.8,0.3) km/s. We have found that components of the Solar velocity are quite insensitive to errors of the distance Ro in a broad range of its values, from Ro=7.5 kpc to Ro=8.5 kpc, that affect the Galactic rotation curve parameters. In the same time, the Solar velocity components(Uo)_{LSR} and (Vo)_{LSR}$ are very sensitive to the Solar radial phase in the spiral density wave.

astro-ph.GA↗

arXiv2013

Orientation Parameters of the Cepheid System in the Galaxy

Based on the distribution of long-period Cepheids, we have redetermined the orientation parameters of their principal plane in the Galaxy. Based on 299 Cepheids with heliocentric distances $r<20$ kpc and pulsation periods $P\geq5^d$, we have found the directions of the three principal axes of the position ellipsoid: $L_1=281.0\pm0.1^\circ,$ $B_1=-1.9\pm0.1^\circ,$ $L_2= 11.0\pm0.7^\circ,$ $B_2=0.2\pm0.1^\circ$ and $L_3=275.9\pm0.7^\circ,$ $B_3=88.1\pm0.1^\circ$. Thus, the line of nodes $l_Ω=L_3+90^\circ=5.9^\circ$ is very close to the direction to the Galactic center; the Cepheid symmetry plane is inclined to the Galactic plane approximately by $-2^\circ$ in the direction of the first axis ($L_1$). The direction of the line of nodes found from old Cepheids ($P<5^d$) differs significantly and is $l_Ω=298^\circ$. The elevation of the Sun above the Galactic plane has been estimated from 365 closer stars ($r<4$ kpc) without any constraint on the pulsation period to be $h_\odot=23\pm5$ pc.

astro-ph.GA↗

arXiv2013

Cepheid Kinematics and the Galactic Warp

The space velocities of 200 long-period ($P>5$ days) classical Cepheids with known proper motions and line-of-sight velocities whose distances were estimated from the period--luminosity relation have been analyzed. The linear Ogorodnikov-Milne model has been applied, with the Galactic rotation having been excluded from the observed velocities in advance. Two significant gradients have been found in the Cepheid velocities, $\partial W/\partial Y=-2.1\pm0.7$ km s$^{-1}$ kpc$^{-1}$ and $\partial V/\partial Z= 27\pm10 $ km s$^{-1}$ kpc$^{-1}$. In such a case, the angular velocity of solid-body rotation around the Galactic $X$ axis directed to the Galactic center is $-15\pm5$ km s$^{-1}$ kpc$^{-1}$.

astro-ph.GA↗

arXiv2013

Galactic Rotation Curve and Spiral Density Wave Parameters from 73 Masers

Based on kinematic data on masers with known trigonometric parallaxes and measurements of the velocities of HI clouds at tangential points in the inner Galaxy, we have refined the parameters of the Allen-Santillan model Galactic potential and constructed the Galactic rotation curve in a wide range of Galactocentric distances, from 0 to 20 kpc. The circular rotation velocity of the Sun for the adopted Galactocentric distance $R_0=8$ kpc is $V_0=239\pm16$ km s$^{-1}$. We have obtained the series of residual tangential, $ΔV_θ$, and radial, $ΔV_R,$ velocities for 73 masers. Based on these series, we have determined the parameters of the Galactic spiral density wave satisfying the linear Lin.Shu model using the method of periodogram analysis that we proposed previously. The tangential and radial perturbation amplitudes are $f_θ=7.0\pm1.2$ km s$^{-1}$ and $f_R=7.8\pm0.7$ km s$^{-1}$, respectively, the perturbation wavelength is $λ=2.3\pm0.4$ kpc, and the pitch angle of the spiral pattern in a two-armed model is $i=-5.2^\circ\pm0.7^\circ$. The phase of the Sun $χ_\odot$ in the spiral density wave is $-50^\circ\pm15^\circ$ and $-160^\circ\pm15^\circ$ from the residual tangential and radial velocities, respectively.

astro-ph.GA↗

arXiv2011

Searching for Possible Siblings of the Sun from a Common Cluster based on Stellar Space Velocities

We propose a kinematic approach to searching for the stars that could be formed with the Sun in a common "parent" open cluster. The approach consists in preselecting suitable candidates by the closeness of their space velocities to the solar velocity and analyzing the parameters of their encounters with the solar orbit in the past in a time interval comparable to the lifetime of stars. We consider stars from the Hipparcos catalog with available radial velocities. The Galactic orbits of stars have been constructed in the Allen--Santillan potential by taking into account the perturbations from the spiral density wave. We show that two stars, HIP 87382 and HIP 47399, are of considerable interest in our problem. Their orbits oscillate near the solar orbit with an amplitude of about 250 pc; there are short-term close encounters to distances <10 pc. Both stars have an evolutionary status and metallicity similar to the solar ones.

astro-ph.SR↗