arXiv subjects

Anisa T. Bajkova

Publications and source records attributed to Anisa T. Bajkova.

At least 19 recordsLinked to original sources

arXiv2026

Analysis of the Space Velocities of Several Samples of Open Star Clusters

An analysis of the kinematics of open star clusters (OSCs) using their characteristics from the new Hunt and Reffert catalog was conducted. Based on 4003 OSCs younger than 200 million years, the following values for the angular velocity of the Galaxy's rotation were found: $Ω_0 = 28.99\pm0.11$ km/s/kpc, $Ω^{'}_0 = -3.909\pm0.026$ km/s/kpc$^{2}$ and $Ω^{''}_0 = 0.5662\pm0.018$ km/s/kpc$^{3}$, where $V_0=234.8\pm3.0$ km/s for $R_0=8.1\pm0.1$ kpc. It was found that periodicity in the radial velocities of OSCs is manifested in clusters younger than 600 Myr, while a wave in residual tangential velocities is observed only in the youngest ones, younger than 40 Myr. A spectral Fourier analysis of the radial velocities of three OSC samples with average ages of 18, 72, and 143 Myr was used to obtain the following values of the wavelength $λ$ and the velocity perturbation amplitude $f_R$: $λ=2.0$ kpc and $f_R=4.3$ km/s, $λ=2.2$ kpc and $f_R=8.2$ km/s, $λ=2.1$ kpc and $f_R=9.6$ km/s, respectively. A systematic change in the positions of the maxima and minima of the waves in the radial velocities of OSCs was found depending on the age of the sample. From the analysis of these shifts, the value of the absolute value of the difference $|ΔΩ|$ between the angular velocity of rotation of the spiral pattern $Ω_p$ and the rotation velocity of the Galaxy was found, $|ΔΩ|=2.0\pm0.5_{stat}\pm2.3_{syst}$ km/s/kpc. Based on this, an estimate of two possible values of the corotation radius was obtained: $8.6\pm0.2$ kpc and $7.6\pm0.2$ kpc, which indicates that the Sun is very close to the corotation.

astro-ph.GA↗

arXiv2026

A study of the spatial evolution of the Radcliffe wave in a sample of young open star clusters

A sample of 139 young open star clusters closely associated with the Radcliffe wave is considered. Modeling their spatial distribution and kinematics over a time interval of 30 Myrs ago and 30 Myrs into the future revealed that they exhibit the main properties characteristic of a Radcliffe wave over the past 10-15 Myr. They are distributed on the galactic XY plane as a long and narrow chain inclined to the Y axis, and exhibit a wave-like behavior of their vertical coordinates up to 15 Myr in the past. This behavior of their vertical coordinates will persist over the interval of 15-20 Myr in the future. A new finding is the presence of vertical perturbations with an amplitude of deviation from the galactic symmetry plane of up to 200 pc over the entire time interval considered in the past, up to -30 Myr. This result calls into question the possibility of using a scenario in which the initial disturbance of the interstellar medium is assumed to be the Parker instability of the galactic magnetic field.

astro-ph.GA↗

arXiv2026

The Spiral Pattern Speed in the Milky Way Galaxy

For a sample of masers, the basic kinematic equations were solved by including the Galactic rotation parameters and the peculiar velocity of the Sun as the unknown variables. Based on spectral analysis, the following estimates were obtained: $|f|_{R,θ}=(7.0,5.1)\pm(1.2,1.4)$ km s$^{-1}$ and the corresponding wavelengths $λ_{R,θ}=(1.9,1.7)\pm(0.4,0.7)$ kpc, as well as $χ_\odot=-140^\circ\pm15^\circ$. The presence of periodic perturbations in the vertical velocities of masers with an amplitude of $|f|_W=3.1\pm1.4$ km s$^{-1}$ and a wavelength of $λ=1.9\pm0.8$ kpc was confirmed. It is shown that the velocities $f_R$ and $f_θ$ can have both the same and different signs. Therefore, we obtained a large scatter of estimates. Thus, if $f_R$ and $f_θ$ have the same signs, then $Ω_p=25.8\pm2.0$ km s$^{-1}$ kpc$^{-1}$ and $R_{cor}=9.1\pm0.8$ kpc. And when $f_R$ and $f_θ$ have different signs, then $Ω_p=35.4\pm2.0$ km s$^{-1}$ kpc$^{-1}$ and $R_{cor}=6.8\pm0.8$ kpc.

astro-ph.GA↗

arXiv2025

Place of the Radcliffe Wave in the Local System

A review of publications devoted to the study of the characteristics of the Radcliffe wave has been given. The advent of mass measurements of radial velocities of stars has recently led to a number of interesting results obtained from the analysis of spatial velocities of stars and open star clusters. An important place in the study has been given to issues related to the clarification of the direct or indirect influence of magnetic fields on the process of formation of the Radcliffe wave. The hypothesis of Parker instability of the galactic magnetic field as one of the reasons for the formation of wave-type inhomogeneities in the galactic disk has been discussed.

astro-ph.GA↗

arXiv2024

Studying the Kinematics of the Stellar Association TW Hya from Current Data

The kinematics of the young stellar association near the Sun TW Hya is studied. Kinematic estimates of the age of this association were obtained in two ways. The first method -- analysis of stellar trajectories integrated back in time -- gave an estimate of the age $t=4.9\pm1.2$ Myr. The second was to analyze the instantaneous velocities of stars and showed that there is a volume expansion of the stellar system with an angular velocity coefficient $K_{xyz}=103\pm12$ km s$^{-1}$ kpc$^{-1}$. Based on this effect, the time interval that passed from the beginning of the expansion of the TW Hya association to the present moment was found, $t=9.5\pm1.1$ Myr. The following principal semi-axes of the residual velocity ellipsoid are determined: $σ_{1,2,3}=(5.25,1.84,0.35)\pm(0.34,0.63,0.26)$ km s$^{-1}$.

astro-ph.GA↗

arXiv2024

Kinematics of Fainst Stars of the Sco-Cen Association According to Gaia Catalog

The kinematic properties of the Sco-Cen association have been studied using the spatial velocities of young stars. New kinematic age estimates for the three components of the association with the age of UCL and LCC being $17.7\pm2.4$ Myrs and the age of US being $6.4\pm1.7$ Myrs have been obtained. The parameters of the residual velocities US, UCL, and LCC ellipsoid have been estimated.

astro-ph.GA↗

arXiv2024

Is the Young Star Association $ε$Cha Double?

The kinematics of the $ε$ Cha young stellar association close to the Sun has been studied based on a list of candidate stars from the Dickson-Vandervelde work. The working sample consists of 26 stars with parallaxes, proper motions from the Gaia~DR3 catalog and radial velocities taken from literary sources. The orbits of the stars back to the past were constructed, and the moment when the association had a minimum spatial size was determined, as well as an analysis of the dependencies of the velocities $U,V,W$ on the coordinates $x,y,z$ was carried out. It is shown that the initial sample is divided into two parts with different kinematic properties. The first sample included 9 stars. Based on the construction of the orbits of these 9 stars, an age estimate of $t=4.9\pm0.8$ million years was obtained. An expansion coefficient in the $xz$ plane with the value $K_{xz}=135\pm19$ km/s/kpc was also found for them, on the basis of which another age estimate $t=7.2\pm1.0$ million years was obtained. The second sample included 17 stars. The construction of their orbits gave an estimate of age $t=0.2\pm0.3$ million years, and based on the gradient $\partial W/\partial z=707\pm248$ km/s/kpc, a second estimate of their age $t=1.4\pm0.5$ million years was obtained. This suggests that the $ε$ Cha association either consists of two groupings of different ages, or a younger one arose as a result of a recent outbreak of star formation within a common star system. The question of the gravitational connection of the groupings has not been considered in the framework of this work.

astro-ph.GA↗

arXiv2024

How common can the origin of clusters Cha I, Cha II, epsilon Cha and eta Cha be?

The trajectories of the clusters $η$ Cha, $ε$ Cha and Cha I, Cha II, constructed backward in time, have been studied. We concluded that the hypothesis about the joint formation of all four of these clusters from one molecular cloud cannot be completely excluded. However, 10-15 Myr ago, all these four clusters were located at approximately the same height above the plane of the Galaxy. Thus, the gas-dust clouds from which all these four clusters were formed were located on one broad front. It is possible that the appearance of the Cha I, Cha II, $ε$ Cha and $η$ Cha clusters may be associated with the impact on such a front of shock waves formed after supernova explosions in the Scorpius-Centauri association. New estimates of the kinematic ages of the clusters Cha I and Cha II are obtained as $0.12\pm0.19$ and $0.05\pm0.15$, respectively. It is shown that the minimum size of the Cha I-north and Cha I-south clusters corresponded to the time of $0.55\pm0.24$ Myr and $0.04\pm0.18$ Myr ago, respectively, and approximately 1.5 Myr ago the distance between the trajectories of these two groupings was minimal.

astro-ph.GA↗

arXiv2024

Globular clusters and bar: captured or not captured?

Studies of the dynamics of globular clusters assume different values of bar parameters (mass, velocity, size) and analyse the results of orbit classifications over the range of the chosen values. It is also a usual thing that a spherical bulge component is converted into the bar to obtain a non-axisymmetric potential from an axisymmetric one. The choice of bar parameters and the way the bar is converted from the bulge introduce systematics into the orbit classifications that we explore in the present study. We integrate orbits of 30 bulge globular clusters residing in the inner area of the Galaxy ($R \lesssim 5$ kpc) backwards in time for three different potentials, two of which are obtained by fitting the rotation curve, and one is taken from the surrogate $N$-body model representing our Galaxy. We analyse each orbit in terms of dominant frequencies obtained from its coordinate spectra. We find that the bar pattern speed is a key factor in orbital classification. With an increase of it, frequencies deviate more and more from the ``bar'' frequency ratio 2:1. The bar-to-bulge mass ratio (assuming the total mass of the bar plus the bulge is fixed) and size of the bar play a smaller role. We also find that, in the $N$-body potential, the fraction of orbits that follow the bar is higher than in those obtained from fitting the rotation curve.

astro-ph.GA↗

arXiv2024

The Radcliffe wave parameters from data on open star clusters

A spectral analysis of the vertical positions and velocities of 374 open star clusters (OSCs) was carried out. We took these OSCs from the Hunt, Reffert catalog; they have an average age of about 10 million years, and are located on the galactic plane XY in a narrow zone inclined by 25 degrees to the galactic axis Y. The following estimates of the parameters of the Radcliffe wave were obtained: a) the maximum value in periodic perturbations of vertical coordinates $Z_{max}=92\pm10$ pc with the wavelength of these perturbations $λ_z=4.82\pm0.09$ kpc; b)~maximum value of the velocity of vertical disturbances $W_{max}=4.36\pm0.12$ km s$^{-1}$ with disturbance wavelength $λ_W=1.78\pm0.02$ kpc. Note that the results of the vertical velocity analysis are first-class in accuracy and completely new.

astro-ph.GA↗

arXiv2023

Peculiarities of Open Star Clusters with High Vertical Velocities from the Region of the Sco-Cen OB Association

We have studied the kinematics of a unique sample of young open star clusters (OSCs) with high vertical velocities, $15<W<40$ km s$^{-1}$. The characteristics of these clusters were taken from the catalogue by Hunt and Reffert (2023), where their mean proper motions, line-of-sight velocities, and distances were calculated using Gaia DR3 data. These OSCs are located within 0.6 kpc of the Sun and form two clumps: one in the region of the Sco-Cen OB association and the other one in the region of the Per OB3-Per OB2 associations. The OSC group of 47 members in the region of the Sco-Cen association is shown to expand along the $y$ axis, $\partial V/\partial y=51\pm12$ km s$^{-1}$ kpc$^{-1}$. This group also has a positive rotation around the $z$ axis with an angular velocity of $71\pm11$ km s$^{-1}$ kpc$^{-1}$ and a negative rotation around the $x$ axis with an angular velocity of $-35\pm5$ km s$^{-1}$ kpc$^{-1}$. Based on the velocities of 27 OSCs from the region of the Per OB3-Per OB2 associations, we have found no gradients differing significantly from zero. We have studied the kinematics of more than 1700 stars selected by Luhman (2022) as probable members of the Sco-Cen OB association. These stars are shown to have no high vertical velocities. The expansion coefficient of the stellar system in the $xy$ plane has been found from all stars to be $K_{xy}=43.2\pm2.2$ km s$^{-1}$ kpc$^{-1}$. Based on stars from the three UCL, LCC, and V1062 Sco groups with a mean age $\sim$20 Myr, for the first time we have found a volume expansion coefficient of the stellar system differing significantly from zero, $K_{xyz}=43.2\pm3.4$ km s$^{-1}$ kpc$^{-1}$.

astro-ph.GA↗

arXiv2023

Determination of the Spiral Pattern Speed in the Milky Way from Young Open Star Clusters

We have estimated the spiral pattern speed in the Galaxy $Ω_p$ from a large sample of young open star clusters (OSCs). For this purpose, we have used 2494 OSCs younger than 50 Myr. Their mean proper motions, line-of-sight velocities, and distances were calculated by Hunt and Reffert (2023) based on data from the Gaia~DR3 catalogue. Three methods have been applied to estimate $Ω_p$. They all are based on the linear Lin-Shu spiral density wave theory. We have obtained an estimate of $Ω_p=24.26\pm0.52$~km s$^{-1}$ kpc$^{-1}$ by the first method, which is most reliable in our view, using the velocity perturbations $f_R$ and $f_θ$ found through a spectral analysis of the radial, $V_R$, and residual rotation, $ΔV_{\rm circ},$ velocities. Using the second method, we have found the velocity perturbations $f_R$ and $f_θ$ by solving the basic kinematic equations together with the Galactic rotation parameters and obtained an estimate of $Ω_p= 23.45\pm0.53$~km s$^{-1}$ kpc$^{-1}$. We have found $Ω_p= 28.9\pm2.8$~km s$^{-1}$ kpc$^{-1}$ by the third method based on an analysis of the position angles of OSCs at their birth time $θ_{\rm birth}$.

astro-ph.GA↗

arXiv2023

Determination of the Spiral Pattern Speed in the Galaxy from Three Samples of Stars

We invoke the estimates of the amplitudes of the velocity perturbations $f_R$ and $f_θ$ caused by the influence of a spiral density wave that have been obtained by us previously from three stellar samples. These include Galactic masers with measured VLBI trigonometric parallaxes and proper motions, OB2 stars, and Cepheids. From these data we have obtained new estimates of the spiral pattern speed in the Galaxy $Ω_p:$ $24.61\pm2.06$, $24.71\pm1.29$ and $25.98\pm1.37$~km s$^{-1}$ kpc$^{-1}$ from the samples of masers, OB2 stars, and Cepheids, respectively. The corotation radii for these three samples $R_{\rm cor}/R_0$ are $1.16\pm0.09$, $1.15\pm0.06$ and $1.09\pm0.06,$ suggesting that the corotation circle is located between the Sun and the Perseus arm segment.

astro-ph.GA↗

arXiv2021

Study of Close Stellar Encounters with the Solar System Based on Data from the Gaia EDR3 Catalogue

We have studied stellar candidates for close (within 1 pc) encounters with the Solar system. For all of the stars under consideration the kinematic characteristics have been taken from the Gaia EDR3 catalogue. The parameters of the encounters of these stars with the Solar system have been calculated using three methods: (1) the linear one, (2) by integrating the orbits in an axisymmetric potential, and (3) by integrating the orbits in a potential with a spiral density wave. All three methods are shown to yield similar results. We have selected five stars that are good candidates for reaching the boundaries of the Oort cloud and passing through it. Based on the second method, in good agreement with the other two methods, we have obtained the following estimates of the encounter parameters for the star GJ 710: $t_{min}=1.320\pm0.028$ Myr and $d_{min}=0.020\pm0.007$ pc. It is also interesting to note the star Gaia EDR3 510911618569239040 with parameters $t_{min}=-2.863\pm0.046$ Myr and $d_{min}=0.057\pm0.079$ pc.

astro-ph.GA↗

arXiv2013

The Milky Way Spiral Structure Parameters from Data on Masers and Selected Open Clusters

To estimate the parameters of the Galactic spiral structure - namely, the pitch angle i and the number of spiral arms,- data on Galactic masers with known trigonometric parallaxes were used. We applied the well-known method based on analysis of the "position angle - distance logarithm" diagram. Estimates of the pitch angle i obtained from four segments of different arms belonging to the global Galactic structure are self-consistent and close to i=-13+/-1 degrees. The segment which is most interesting is that of the Outer arm. It contains only three masers. Hence, in order to obtain correct estimates, we also used the data on 12 very young star clusters with distances determined by Camargo et al. from infrared photometry. The estimates obtained allow us to conclude in favor of the four-armed model of the Galactic spiral structure.

astro-ph.GA↗

arXiv2011

Multi-frequency synthesis algorithm based on Generalized Maximum Entropy Method. Application to 0954+658

We propose the multi-frequency synthesis (MFS) algorithm with spectral correction of frequency-dependent source brightness distribution based on maximum entropy method. In order to take into account the spectral terms of n-th order in the Taylor expansion for the frequency-dependent brightness distribution, we use a generalized form of the maximum entropy method suitable for reconstruction of not only positive-definite functions, but also sign-variable ones. The proposed algorithm is aimed at producing both improved total intensity image and two-dimensional spectral index distribution over the source. We consider also the problem of frequency-dependent variation of the radio core positions of self-absorbed active galactic nuclei, which should be taken into account in a correct multi-frequency synthesis. First, the proposed MFS algorithm has been tested on simulated data and then applied to four-frequency synthesis imaging of the radio source 0954+658 from VLBA observational data obtained quasi-simultaneously at 5, 8, 15 and 22 GHz.

astro-ph.CO↗

arXiv2011

Multifrequency VLBA study of the blazar S5 0716+714 during the active state in 2004 II. Large-scale jet kinematics and the comparison of the different methods of VLBI data imaging as applied to kinematic studies of AGN

We study the jet kinematics of the blazar S5 0716+714 during its active state in 2003-2004 with multi-epoch VLBI observations. Aims. We present a kinematic analysis of the large-scale (0-12 mas) jet of 0716+714, based on the results of six epochs of VLBA monitoring at 5 GHz. Additionally, we compare kinematic results obtained with two imaging methods based on different deconvolution algorithms. The blazar 0716+714 has a diffuse large-scale jet and a very faint bright compact core. Experiments with simulated data showed that the conventional data reduction procedure based on the CLEAN deconvolution algorithm does not perform well in restoring this type of structure. This might be the reason why previous kinematic studies of this source yielded ambiguous results. In order to obtain accurate kinematics of this source, we independently applied two imaging techniques to the raw data: the conventional method, based on difference mapping, which uses CLEAN deconvolution, and the generalized maximum entropy method (GMEM) realized in the VLBImager package developed at the Pulkovo Observatory in Russia. The results of both methods give us a consistent kinematic scenario: the large-scale jet of 0716+714 is diffuse and stationary. Differences between the inner (0-1 mas) and outer (1-12 mas) regions of the jet in brightness and velocity of the components could be explained by the bending of the jet, which causes the angle between the jet direction and the line of sight to change from ~5 deg to ~11 deg. For the source 0716+714 both methods worked at the limit of their capability.

astro-ph.CO↗

arXiv2010

Multifrequency Method for Mapping Active Galactic Nuclei with Allowance for the Frequency-Dependent Image Shift

We consider the problem of multifrequency VLBA image synthesis and spectral-index mapping for active galactic nuclei related to the necessity of taking into account the frequency-dependent image shift. We describe our generalized multifrequency synthesis algorithm with a spectral correction based on the maximum entropy method. The results of our processing of multifrequency VLBI data for the radio sources J2202+4216, J0336+3218, and J1419+5423 are presented.

astro-ph.CO↗