arXiv subjects

V. V. Bobylev

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

At least 37 records · Page 2Linked to original sources

arXiv2022

Kinematics of OB Stars with Data from the LAMOST and Gaia Catalogues

We have analyzed the kinematics of OB stars from the list by Xiang et al. (2021) that contains $\sim$13 000 single OB stars. For these stars there are photometric distance estimates and proper motions from the Gaia catalogue and line-of-sight velocities from the LAMOST catalogue. Based on a sample of single OB stars and using the photometric distances and proper motions of stars from the Gaia EDR3 catalogue, we have found the group velocity components $(U_\odot,V_\odot,W_\odot)=(9.63,9.93,7.45)\pm(0.27,0.34,0.10)$ km s$^{-1}$, and the following parameters of the angular velocity of Galactic rotation: $Ω_0=29.20\pm0.18$ km s$^{-1}$ kpc$^{-1}$, $Ω^{'}_0=-4.150\pm0.046$ km s$^{-1}$ kpc$^{-2}$ and $Ω^{''}_0=0.795\pm0.018$ km s$^{-1}$ kpc$^{-3}$, where the error per unit weight $σ_0$ is 9.56 km s$^{-1}$ and $V_0=236.5\pm3.3$ km s$^{-1}$ (for the adopted $R_0=8.1\pm0.1$ kpc). Based on the same OB stars, we have found the residual velocity dispersions $(σ_1,σ_2,σ_3)=(15.13,9.69,7.98)\pm(0.07,0.05,0.04)$ km s$^{-1}$. We show that using the line-of-sight velocities increases significantly the space velocity dispersion and leads to a biased estimate of the velocity $U_\odot$. A comparison of the distances scales used has shown that the photometric distances from Xiang et al. (2021) should be lengthened approximately by 10%.

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arXiv2022

Estimation of the Parameters of the Spiral Pattern in the Galaxy Based on a Sample of Classical Cepheids

We consider a sample of Galactic classical Cepheids with highly accurate estimates of their distances taken from Skowron et al., where they were determined based on the period-luminosity relation. We have refined the geometric characteristics of two spiral arm segments-the Carina-Sagittarius and Outer ones. For this purpose, we have selected 269 Cepheids belonging to the Carina-Sagittarius arm with ages in the range 80-120 Myr. From them we have estimated the pitch angle of the spiral pattern $i=-11.9\pm0.2^\circ$ and the position of this arm $a_0=7.32\pm0.05$ kpc for the adopted $R_0=8.1\pm0.1$ kpc. In the Outer arm we have selected 343 Cepheids with ages in the range 120-300 Myr. From them we have found $i=-11.5\pm0.5^\circ$ and $a_0=12.89\pm0.06$ kpc. Adhering to the model of a grand-design spiral pattern in the Galaxy with one pitch angle for all arms, we can conclude that this angle is close to $-12^\circ$.

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arXiv2022

Galaxy Rotation Parameters from OB2 Stars with Proper Motions and Parallaxes from the Gaia EDR3 Catalog

We have analyzed the kinematics of OB2 stars with proper motions and parallaxes selected by Xu et al. from the Gaia EDR3 catalog. The relative parallax errors for all the stars in this sample do not exceed 10\%. Based on a sample of 9750 stars, the group velocity components $(U,V,W)_\odot=(7.21,7.46,8.52)\pm(0.13,0.20,0.10)$~km/s were obtained and the parameters of the angular velocity of rotation of the Galaxy: $Ω_0 =29.712\pm0.062$~km/s/kpc, $Ω^{'}_0=-4.014\pm0.018$~km/s/kpc$^{2}$ and $Ω^{''}_0=0.674\pm0.009$~km/s/kpc$^{3}$. The circular velocity of rotation of the solar neighborhood around the center of the Galaxy is $V_0=240.7\pm3.0$~km/s for the assumed distance of the Sun to the galactic center $R_0=8.1\pm0.1$~kpc. It is shown that the influence of the systematic correction to the trigonometric parallaxes of the Gaia EDR3 catalog with the value $Δπ=-0.040$~mas does not exceed the $\sim1σ$ level of the errors of the sought-for kinematic parameters of the model. Based on the proper motions of OB stars, the following variances of the residual velocities were found: $(σ_1,σ_2,σ_3)=(11.79,9.66,7.21)\pm(0.06,0.05,0.04)$~km/s. It is shown that the first axis of this ellipsoid slightly deviates from the direction to the center of the Galaxy $L_1=12.4\pm0.1^\circ$, and the third axis is oriented almost exactly to the north pole of the Galaxy, $B_3=87.7\pm0.1^\circ.$

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arXiv2022

Kinematics of the Galaxy from Young Open Star Clusters with Data from the Gaia EDR3 Catalogue

We have analyzed the kinematics of open star clusters (OSCs) with the proper motions and distances calculated by Hao et al. based on Gaia EDR3 data. The mean line-of-sight velocities are known for a number of clusters from this list. We show that the Galactic rotation parameters determined from samples of OSCs with various ages are in good agreement between themselves. The most interesting results have been obtained from a sample of 967 youngest OSCs with a mean age of 18 Myr. In particular, we have found the following parameters of the angular velocity of Galactic rotation using only their proper motions and distances: $Ω_0 =28.01\pm0.15$ km s$^{-1}$ kpc$^{-1},$ $Ω^{'}_0=-3.674\pm0.040$ km s$^{-1}$ kpc$^{-2},$ and $Ω^{''}_0=0.565\pm0.023$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center here is $V_0=226.9\pm3.1$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.1\pm0.1$ kpc. The parameters of the spiral density wave have been determined from the space velocities of 233 young clusters. The amplitudes of the radial and tangential velocity perturbations produced by the spiral density wave are $f_R=9.1\pm0.8$ km s$^{-1}$ and $f_θ=4.6\pm1.2$ km s$^{-1}$, respectively; the perturbation wavelengths are $λ_R=3.3\pm0.5$ kpc and $λ_θ=2.6\pm0.6$ kpc for the the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave has been found to be $(χ_\odot)_R\approx-180^\circ$.

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arXiv2021

Estimation of the Radial Scale Length and Vertical Scale Height of the Galactic Thin Disk from Cepheids

Up-to-date data on 2214 classical Cepheids have been used. The model of an exponential matter density distribution in the Galactic thin disk has been applied. New estimates of the radial disk scale length $h_R,$ the distance of the Sun from the symmetry plane $z_\odot$, and the vertical disk scale height $h_z$ have been obtained. Based on samples of 1087 Cepheids younger than 120 Myr and 1127 Cepheids older than 120 Myr, we have found $h_R=2.30\pm0.09$ kpc and $h_R=1.96\pm0.12$ kpc, respectively. It has turned out that an unambiguous estimate of $h_R$ cannot be obtained from their overall radial distribution. However, we have constructed the radial distribution of 806 Cepheids of different ages at the time of their birth from which we have found $h_R=2.36\pm0.24$ kpc. We show that $h_z$ depends strongly on the age of stars. For example, from 705 Cepheids younger than 120 Myr with heliocentric distances $r<6$ kpc we have found $z_\odot=-17\pm4$ pc and $h_z=75\pm5$ pc. From 393 Cepheids older than 120 Myr at $r<6$ kpc, we have found $z_\odot=-39\pm11$ pc and $h_z=131\pm10$ pc.

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arXiv2021

Study of the Influence of an Evolving Galactic Potential on the Orbital Properties of 152 Globular clusters with Data from the Gaia EDR3 Catalogue

We have studied the influence of an evolving gravitational potential of the Milky Way Galaxy on the orbital motion of 152 globular clusters with proper motions from the Gaia EDR3 catalogue and mean distances from Baumgardt and Vasiliev (2021). To construct a semicosmological evolving model potential with changing masses and sizes of the Galactic components, we have used the algorithm described in Haghi et al. (2015). The adopted axisymmetric three-component model potential of the Galaxy includes a spherical bulge, a flat Miyamoto--Nagai disk, and a spherical Navarro--Frenk--White dark matter halo.The orbits are integrated backward in time. We compare the orbital parameters of globular clusters derived in static and evolving potentials when integrating the orbits for 5 and 12 Gyr backward. For the first time we have studied the influence of separately a change in the masses and a change in the sizes of the Galactic components. The changes in the masses and sizes of the components are shown to act on the orbital parameters in the opposite way. At small Galactocentric distances this influence is maximally compensated for. The orbits of distant globular clusters and those with a large apocenter distance undergo the biggest changes. We show that on time scales up to $-5$~Gyr the orbits of globular clusters in the case of a potential with both changing masses and changing sizes of the components undergo, on average, minor changes compared to the case of a static potential. These changes fit into the limits of the statistical uncertainties caused by the errors in the data. So, on these time scales the Galactic potential may be deemed static. We provide tables with the orbital parameters of globular clusters derived in both static and evolving potentials.

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arXiv2021

Comparison of the Orbital Properties of the Milky Way Globular Clusters from the Data of the Gaia DR2 and EDR3 Catalogs

We provide new values of the orbital parameters of 152 globular clusters, which are calculated using the new mean proper motions obtained from the Gaia EDR3 catalog data. The orbits were integrated 5 Gyr back in an axisymmetric three-component potential with a spherical bulge, disk component, and spherical dark halo in the Navarro-Frenk-White form, which we refined using the rotation curve of objects with large galactocentric distances up to 200 kpc. The obtained orbital parameters were compared with the orbital parameters of the same globular clusters calculated earlier in the same gravitational potential using proper motions from the Gaia DR2 catalog data. The objects whose orbits underwent significant changes were identified.

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arXiv2021

Analysis of Selected Runaway Stars in the Orion Nebula Based on Data from the Gaia EDR3 Catalogue

We have performed Monte Carlo simulations of the trajectories of several runaway stars using their parallaxes and proper motions from the Gaia EDR3 catalogue. We have confirmed the hypothesis that the stars AE Aur and $μ$Col are a product of the multiple system breakup $\sim$2.5 Myr ago and the Orion Trapezium may be the parent cluster for this pair of stars. We show that the data from the Gaia EDR3 catalogue for the star $ι$Ori, mainly the parallax, do not allow us to talk about the breakup of the multiple system of AE Aur, $μ$Col, and $ι$Ori. The existence of close pair encounters between the stars HD 30112 and HD 43112 $\sim$1 Myr ago has been confirmed. Close triple encounters confirm the hypothesis that the stars HD 30112 and HD 43112 escaped from the parent cluster Col 69. We show that the stars HIP 28133 and TYC 5368-1541-1 have a nonzero probability of escape from the region within 10 pc of the center of the Orion Trapezium cluster and a fairly high probability (about 8\%) that they were both at distances less than 20 pc from the center of the Orion Trapezium $\sim$2.5 Myr ago. It has been established for the first time that the stars Gaia EDR3 3021115184676332288 and Gaia EDR3 2983790269606043648 have a probability of about 0.5\% that they broke up as a binary system $\sim$1.1 Myr ago. The star Gaia EDR3 3021115184676332288 has a probability of about 16\% that it escaped from the region within 10 pc of the center of the Orion Trapezium cluster $\sim$1 Myr ago.

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arXiv2021

A New Estimate of the Best Value for the Solar Galactocentric Distance

Using data from the literature, we made a list of individual estimates of the solar Galactocentric distance, which were performed after 2017 by different methods. These values have not yet been used to calculate the best value of mean $R_0$. For the sample containing 21 estimates, based on the standard approach, we found the weighted mean ${\overline R_0}=8.14$ kpc with the dispersion $σ=0.16$ kpc, and using the median statistics, we obtained the estimate $R_0=8.15\pm0.11$ kpc. For practical use, the value $R_0=8.1\pm0.1$ kpc can be recommended.

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arXiv2021

Orbits of 152 Globular Clusters of the Milky Way Galaxy Constructed from the Gaia DR2 data

We present orbits and their properties for 152 globular clusters of the Milky Way galaxy obtained using average Gaia DR2 proper motions and other astrometric data from the list of Vasiliev (2019). For orbit integrating we have used the axisymmetric model of the Galactic potential based on the Navarro-Frenk-White dark halo, and modified by Bajkova and Bobylev (2016) using circular velocities of Galactic objects in wide region of Galactocentric distances (up to 200 kpc) from Bhattacharjee et.al. (2014) catalog. Based on the analysis of the obtained orbits, we have modified the composition of the subsystems of globular clusters presented in Massari et. al. (2019).

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arXiv2021

Analysis of galaxy kinematics based on Cepheids from the Gaia DR2 Catalogue

To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalog are used in large part. The working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at a solar distance is $V_0=240\pm3$~km s$^{-1}$. In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be $R_0=8.27\pm0.10$~kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at present time and in the past. So, the value of the wavelength $λ_{R,θ}$ is in the range of [2.4--3.0] kpc, the pitch angle $i_{R,θ}$ is in the range of [$-13^\circ$,$-10^\circ$] for a four-arm pattern model, the amplitudes of the radial and tangential perturbations are $f_R\sim12$~km s$^{-1}$ and $f_θ\sim9$~km s$^{-1}$, respectively. Velocities of Cepheids older than 120 Myr are currently giving a wavelength $λ_{R,θ}\sim5$~kpc. This value differs significantly from one that we obtained from the samples of young Cepheids. An analysis of positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength $λ_{R,θ}=2.7$~kpc, amplitudes of radial and tangential perturbations are $f_R=7.9$~km s$^{-1}$ and $f_θ=5$~km s$^{-1}$, respectively.

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arXiv2020

Orbits of 47 Dwarf Satellite Galaxies of the Milky Way in Three Models of the Gravitational Potential with Different Masses

The analysis of the orbits of 47 dwarf satellite galaxies of the Milky Way, built using three models of the Galactic gravitational potential with different masses, is presented. The models of the Galactic potential were chosen based on the analysis of a large number of the Galaxy mass estimates known from the literature. The astrometric data needed for calculation of the initial positions and velocities (6D phase space) of the dwarf galaxies are also taken from the literature, where the average proper motions were determined on the basis of the data from the Gaia DR2 Catalog. We present the orbits and their properties of all 47 dwarf galaxies obtained by integration for 13.5 Gyr backward in all three models of the Galactic potential and give a comparison of the orbital parameters. For each model of the Galactic potential we have identified dwarf galaxies that are not connected gravitationally with the Milky Way.

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arXiv2020

Kinematic Properties of Young Intermediate- and Low-Mass Stars from the Gaia DR2 Catalogue

We have studied the kinematic properties of young pre-main-sequence stars. We have selected these stars based on data from the Gaia DR2 catalogue by invoking a number of photometric infrared surveys. Using 4564 stars with parallax errors less than 20\%, we have found the following parameters of the angular velocity of Galactic rotation: $Ω_0 =28.84\pm0.10$ km s$^{-1}$ kpc$^{-1}$, $Ω^{'}_0=-4.063\pm0.029$ km s$^{-1}$ kpc$^{-2}$ and $Ω^{''}_0=0.766\pm0.020$ km s$^{-1}$ kpc$^{-3}$, where the Oort constants are $A=16.25\pm0.33$ km s$^{-1}$ kpc$^{-1}$ and $B=-12.58\pm0.34$ km s$^{-1}$ kpc$^{-1}$. The circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=230.7\pm4.4$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc. The residual velocity dispersion for the stars considered is shown to be low, suggesting that they are extremely young. The residual velocity dispersion averaged over three coordinates is $\sim$11 km s$^{-1}$ for Herbig Ae/Be stars and $\sim$7 km s$^{-1}$ for T Tauri stars.

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arXiv2020

Study of the Galactic Rotation Based on Masers and Radio Stars with VLBI Measurements of Their Parallaxes

Based on published data, we have produced a sample of 256 radio sources whose trigonometric parallaxes and proper motions were measured by VLBI. This sample contains Galactic masers associated with massive protostars and stars in active star-forming regions. It also includes young low-mass stars from the Gould Belt region whose radio observations were performed in continuum. Based on this, most complete sample of sources to date, we have estimated the velocities $(U,V,W)_\odot$ and the parameters of the angular velocity of Galactic rotation $Ω_0, Ω^{(1)}_0, ... , Ω^{(4)}_0$ and obtained a new estimate of the distance fromthe Sun to the Galactic center, $R_0=8.15^{+0.04}_{-0.20}$ kpc. The parameters of the Galactic spiral density wave have been found from the series of radial, $V_R$, and residual tangential, $ΔV_{circ}$, velocities of stars. The amplitudes of the radial and tangential velocity perturbations are $f_R=7.0\pm0.9$ km s$^{-1}$ and $f_θ=3.8\pm1.1$ km s$^{-1}$, the perturbation wavelengths are $λ_R=2.3\pm0.2$ kpc and $λ_θ=2.0\pm0.4$ kpc, and the Sun's phases in the spiral density wave are $(χ_\odot)_R=-163^\circ\pm9^\circ$ and $(χ_\odot)_θ=-137^\circ\pm10^\circ$ for the adopted four-armed spiral pattern.

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arXiv2020

Kinematics of pre-main sequence stars from the Gaia DR2 catalog

The kinematic properties of young stars that have not yet reached the stage of the main sequence are studied. The selection of these stars was recently carried out by Marton et al. (2019) and Vioque et al. (2020) according to the Gaia DR2 catalog using a number of photometric infrared surveys. We have determined the rotation parameters of the Galaxy and the parameters of the ellipsoids of the residual velocities. The linear velocity of the circular rotation of a solar region around the center of the Galaxy, found using 4431 stars, is equal to V_0=229.1+-4.4 km/s. The following ellipsoid parameters of their residual velocities are found from low-mass stars (of type T Tau): $σ_{1,2,3}=(9.45,6.99,6.61)\pm(0.94,0.43,0.32)$ km/s. For stars of intermediate masses (Herbig Ae/Be stars), their values turned out to be somewhat larger $σ_{1,2,3}=(13.67,9.25,7.26)\pm(2.40,2.44,0.88)$ km/s. Distant stars from both Catalogs trace the local spiral arm well. For 1212 stars, a new estimate of the pitch angle of the Local spiral arm is equal to i=-8.9+-0.1 deg.

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arXiv2020

Galactic Rotation Parameters Based on Stars from Activ Star-Forming Regions with Data from the Gaia DR2 Catalogue

We have studied a sample of more than 25 000 young stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The relative errors of their parallaxes do not exceed 10\%. The selection of stars belonging to active star-forming regions was made by Marton et al. based on data from the Gaia DR2 catalogue by invoking infrared measurements from the WISE and Planck catalogues. Low-mass T Tauri stars constitute the majority of sample stars. The following parameters of the angular velocity of Galactic rotation have been found from them: $Ω_0 =28.40\pm0.11$ km s$^{-1}$ kpc$^{-1}$, $Ω^{'}_0=-3.933\pm0.033$ km s$^{-1}$ kpc$^{-2}$ and $Ω^{''}_0=0.804\pm0.040$ km s$^{-1}$ kpc$^{-3}$. The Oort constants are $A=15.73\pm0.32$ km s$^{-1}$ kpc$^{-1}$ and $B=-12.67\pm0.34$ km s$^{-1}$ kpc$^{-1}$, while the circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=227\pm4$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc.

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arXiv2020

Estimation of the Gould Belt scale height from T Tauri type stars in the Gaia DR2 catalogue

We analyze the spatial and kinematic properties of a large sample of young T Tauri type stars in a 500 pc radius solar neighborhood, closely related to the Gould belt. The following parameters of the exponential density distribution have been determined: the average $(z_G)_\odot=-25\pm5$ pc and scale height $h_G=56\pm6$ pc. We propose a method of excluding background stars from the samples, which are located at large heights with respect to the symmetry plane of the Gould belt. We discovered that the expansion effect for the entire star system, $K_G=6\pm1$ km s$^{-1}$ kpc$^{-1}$, is determined mainly by the dynamics of the Scorpius-Centaurus association. We show that the angular velocity of the residual intrinsic rotation of the Gould belt can reach $Ω_G=6.9\pm0.2$ km s$^{-1}$ kpc$^{-1}$ and that this rotation is opposite to the galactic rotation.

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arXiv2020

Analysis of Close Stellar Encounters with the Solar System

We consider 36 candidates for close (within 1 pc) encounters with the Solar system. These stars have been selected in accordance with the results of an analysis of their motion obtained by various authors. For most stars from this list the kinematic characteristics have been taken from the Gaia DR2 catalogue. The parameters of the encounters of these stars with the Solar system have been calculated using three methods: (1) the linear one, (2) the epicyclic one, and (3) by integrating the orbits in an axisymmetric potential. We have concluded that the epicyclic method works quite well only on a time interval no longer than $\pm$1 Myr. Based on the third method, in good agreement with the first method, for the first time we have obtained the following estimates of the encounter parameters for the star Gaia DR2 3130033734235815424: $t_{min}=-0.62\pm0.12$ Myr and $d_{min}=0.30\pm0.10$ pc.

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