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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., 10 pages, 4 tables and 0 figures. arXiv admin note: substantial text overlap with arXiv:2006.16555

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 $\Omega_0, \Omega^{(1)}_0, ... , \Omega^{(4)}_0$ 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, $\Delta V_{circ}$, velocities of stars. The amplitudes of the radial and tangential velocity perturbations are $f_R=7.0\pm0.9$ km s$^{-1}$ and $f_\theta=3.8\pm1.1$ km s$^{-1}$, the perturbation wavelengths are $\lambda_R=2.3\pm0.2$ kpc and $\lambda_\theta=2.0\pm0.4$ kpc, and the Sun's phases in the spiral density wave are $(\chi_\odot)_R=-163^\circ\pm9^\circ$ and $(\chi_\odot)_\theta=-137^\circ\pm10^\circ$ for the adopted four-armed spiral pattern., Comment: 13 pages, 6 figures, 1 table. arXiv admin note: text overlap with arXiv:1903.09313, arXiv:1906.10151

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: $\Omega_0 =28.40\pm0.11$ km s$^{-1}$ kpc$^{-1}$, $\Omega^{'}_0=-3.933\pm0.033$ km s$^{-1}$ kpc$^{-2}$ and $\Omega^{''}_0=0.804\pm0.040$ 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., Comment: 12 pages, 4 figures, 4 tables

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., 14 pages, 2 Figures, 4 Tables

We have studied the kinematic properties of the candidates for hot subdwarfs (HSDs) selected by Geier et al. from the Gaia DR2 catalogue. We have used a total of 12 515 stars with relative trigonometric parallax errors less than 30\%. The HSDs are shown to have different kinematics, depending on their positions on the celestial sphere. For example, the sample of low-latitude $(|b, Comment: 18 pages, 4 figures, 4 tables

We have selected a sample of 326 young $(\log t, Comment: 14 pages, 5 figures. arXiv admin note: text overlap with arXiv:1809.10512, arXiv:1609.08341

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 $\mu$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 $\iota$Ori, mainly the parallax, do not allow us to talk about the breakup of the multiple system of AE Aur, $\mu$Col, and $\iota$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., Comment: 15 pages, 9 figures, 3 tables

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. For orbital integration we have applied the axisymmetric model of the Galactic potential based on the Navarro-Frenk- White dark halo, and modified by Bajkova & Bobylev utilizing circular velocities of Galactic objects in a wide region of Galactocentric distances (up to 200 kpc) from the Bhattacharjee et al. 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.

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 p⊙ - 0.1M⊙ pc−3 and the vertical force |Kz=1.1|/2πG = 77M⊙ 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.

We consider open star clusters (OSCs) with the proper motions, parallaxes, and line-of-sight velocities calculated by various authors from Gaia DR2 data. The distance scale factor has been found by analyzing the separate solutions of the basic kinematic equations to be $p=1.00\pm0.04.$ It shows that the distances calculated using the parallaxes from the Gaia DR2 catalogue do not need any correction factor. We have investigated the solutions obtained from various OSC samples differing in both age and accuracy of their parallax and line-of-sight velocity measurements. The solution obtained from a sample of 930 OSCs satisfying the constraints on the age logt, Comment: 12 pages, 1 figure, 2 tables. arXiv admin note: text overlap with arXiv:1903.09313

We have studied a sample containing about 6000 OB stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The following parameters of the angular velocity of Galactic rotation have been found: $\Omega_0=29.70\pm0.11$ km s$^{-1}$ kpc$^{-1}$, $\Omega'_0=-4.035\pm0.031$ km s$^{-1}$ kpc$^{-2}$, and $\Omega''_0= 0.620\pm0.014$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=238\pm5$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc. The amplitudes of the tangential and radial velocity perturbations produced by the spiral density wave are $f_\theta=4.4\pm1.4$ km s$^{-1}$ and $f_R=5.1\pm1.2$ km s$^{-1}$, respectively; the perturbation wavelengths are $\lambda_\theta=1.9\pm0.5$ kpc and $\lambda_R=2.1\pm0.5$ kpc for the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave is $\chi_\odot=-178^\circ\pm12^\circ$., Comment: 14 pages, 2 tables, 4 figures. arXiv admin note: substantial text overlap with arXiv:1903.09313, arXiv:1904.12686, arXiv:1809.10512, arXiv:1609.08341

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, 22 pages, 7 figures, 2 tables

We have identified the four most significant features in the UV velocity distribution of solar neighborhood stars: H1, H2 in the Hercules stream and W1, W2 in the Wolf 630 stream. We have formulated the problem of determining several characteristics of the central Galactic bar independently from each of the identified features by assuming that the Hercules and Wolf 630 streams are of a bar-induced dynamical nature. The problem has been solved by constructing 2:1 resonant orbits in the rotating bar frame for each star in these streams. Analysis of the resonant orbits found has shown that the bar pattern speed is 45-55 km/s/kpc, while the bar angle lies within the range 40-60 degrees. The results obtained are consistent with the view that the Hercules and Wolf 630 streams could be formed by a long-term influence of the Galactic bar leading to a characteristic bimodal splitting of the UV velocity plane., Comment: 16 pages, 3 tables, 5 figures

We compiled published data on Galactic masers with VLBI-measured trigonometric parallaxes and determined the residual tangential, ∆V circ, and radial, ∆VR , velocities for 120 masers. We used these data to redetermine the parameters of the Galactic spiral density wave using the method of spectral analysis. The most interesting result of this study is the detection of wavelike oscillations of vertical spatial velocities (W) versus distance R from the Galactic rotation axis. Spectral analysis allowed us to determine the perturbation wavelength and the amplitude of this wave, which we found to be equal to λ W = 3.4 ± 0.7 kpc and fW = 4.9 ± 1.2 km s−1, respectively.

We have selected and analyzed a sample of OB stars with known line-of-sight velocities determined through ground-based observations and with trigonometric parallaxes and proper motions from the Gaia DR2 catalogue. Some of the stars in our sample have distance estimates made from calcium lines. A direct comparison with the trigonometric distance scale has shown that the calcium distance scale should be reduced by 13\%. The following parameters of the Galactic rotation curve have been determined from 495 OB stars with relative parallax errors less than 30\%: $(U,V,W)_\odot=(8.16,11.19,8.55)\pm(0.48,0.56,0.48)$ km s$^{-1}$, $\Omega_0=28.92\pm0.39$ km s$^{-1}$ kpc$^{-1}$, $\Omega^{'}_0=-4.087\pm0.083$ km s$^{-1}$ kpc$^{-2}$ and $\Omega^{''}_0=0.703\pm0.067$ km s$^{-1}$ kpc$^{-3}$, where the circular velocity of the local standard of rest is $V_0=231\pm5$ km s$^{-1}$ (for the adopted $R_0=8.0\pm0.15$ kpc). The parameters of the Galactic spiral density wave have been found from the series of radial, $V_R,$ residual tangential, $\Delta V_{circ}$, and vertical, $W,$ velocities of OB stars by applying a periodogram analysis. The amplitudes of the radial, tangential, and vertical velocity perturbations are $f_R=7.1\pm0.3$ km s$^{-1}$, $f_\theta=6.5\pm0.4$ km s$^{-1}$, and $f_W=4.8\pm0.8$ km s$^{-1}$, respectively; the perturbation wavelengths are $ \lambda_R=3.3\pm0.1$ kpc, $\lambda_\theta=2.3\pm0.2$ kpc, and $ \lambda_W=2.6\pm0.5$ kpc; and the Sun's radial phase in the spiral density wave is $ (\chi_\odot)_R=-135\pm5^\circ$, $(\chi_\odot)_\theta=-123\pm8^\circ$, and $ (\chi_\odot)_W=-132\pm21^\circ$ for the adopted four-armed spiral pattern., Comment: 16 pages,6 figures, 1 table

We consider young distant stars from the Gaia TGAS catalog. These are 250 classical Cepheids and 244 OB stars located at distances up to 4 kpc from the Sun. These stars are used to determine the Galactic rotation parameters using both trigonometric parallaxes and proper motions of the TGAS stars. In this case the considered stars have relative parallax errors less than 200%. Following the well-known statistical approach, we assume that the kinematic parameters found from the line-of-sight velocities $V_r$ are less dependent on errors of distances than the found from the velocity components $V_l$. From values of the first derivative of the Galactic rotation angular velocity $\Omega{'}_0$, found from the analysis of velocities $V_r$ and $V_l$ separately, the scale factor of distances is determined. We found that from the sample of Cepheids the scale of distances of the TGAS should be reduced by 3%, and from the sample of OB stars, on the contrary, the scale should be increased by 9%., Comment: 5 pages, 1 figure, 2 tables

We have studied the simultaneous and separate solutions of the basic kinematic equations obtained using the stellar velocities calculated on the basis of data from the Gaia TGAS and RAVE5 catalogues. By comparing the values of Omega_0' found by separately analyzing only the line-of-sight velocities of stars and only their proper motions, we have determined the distance scale correction factor p to be close to unity, 0.97+/-0.04. Based on the proper motions of stars from the Gaia TGAS catalogue with relative trigonometric parallax errors less than 10% (they are at a mean distance of 226 pc), we have found the components of the group velocity vector for the sample stars relative to the Sun (U,V,W)o=(9.28,20.35,7.36)+/-(0.05,0.07,0.05) km s^{-1}, the angular velocity of Galactic rotation Omega0=27.24+/-0.30 km s^{-1} kpc^{-1}, and its first derivative Omega_0'=-3.77+/-0.06 km s^{-1} kpc^{-2}; here, the circular rotation velocity of the Sun around the Galactic center is V_0=218+/-6 km s^{-1} kpc (for the adopted distance R_0=8.0+/-0.2 kpc), while the Oort constants are A=15.07+/-0.25 km s^{-1} kpc^{-1} and B=-12.17+/-0.39 km s^{-1} kpc^{-1}, p=0.98+/-0.08. The kinematics of Gaia TGAS stars with parallax errors more than 10% has been studied by invoking the distances from a paper by Astraatmadja and Bailer-Jones that were corrected for the Lutz-Kelker bias. We show that the second derivative of the angular velocity of Galactic rotation Omega_0"=0.864+/-0.021 km s^{-1} kpc^{-3} is well determined from stars at a mean distance of 537 pc. On the whole, we have found that the distances of stars from the Gaia TGAS catalogue calculated using their trigonometric parallaxes do not require any additional correction factor., Comment: 11 pages, 1 figure, 5 tables

We have analyzed the space velocities of stars with the proper motions and trigonometric parallaxes from the Gaia TGAS catalogue in combination with the line-of-sight velocities from the RAVE5 catalogue. In the (V,\sqrt{U^2+2V^2}) velocity plane we have identified three clumps, BB17-1, BB17-2, and BB17-3, in the region of large velocities (V, Comment: 12 pages, 4 figures, 1 table

We have searched for the stars that either encountered in the past or will encounter in the future with the Solar system closer than 2 pc. For this purpose, we took more than 216 000 stars with the measured proper motions and trigonometric parallaxes from the Gaia DR1 catalogue and their radial velocities from the RAVE5 catalogue. We have found several stars for which encounters closer than 1 pc are possible. The star GJ 710, for which the minimum distance is d_m=0.063+/-0.044 pc at time t_m=1385+/-52 thousand years, is the record-holder among them. Two more stars, TYC 8088-631-1 and TYC 6528-980-1, whose encounter parameters, however, are estimated with large errors, are of interest., 11 pages, 2 figures, 3 tables

The catalogue of protoplanetary nebulae by Vickers et al. has been supplemented with the line-of-sight velocities and proper motions of their central stars from the literature. Based on an exponential density distribution, we have estimated the vertical scale height from objects with an age less than 3 Gyr belonging to the Galactic thin disk (luminosities higher than 5000 Lo) to be h=146+/-15 pc, while from a sample of older objects (luminosities lower than 5000 Lo) it is h=568+/-42 pc. We have produced a list of 147 nebulae in which there are only the line-of-sight velocities for 55 nebulae, only the proper motions for 25 nebulae, and both line-of-sight velocities and proper motions for 67 nebulae. Based on this kinematic sample, we have estimated the Galactic rotation parameters and the residual velocity dispersions of protoplanetary nebulae as a function of their age. We have established that there is a good correlation between the kinematic properties of nebulae and their separation in luminosity proposed by Vickers. Most of the nebulae are shown to be involved in the Galactic rotation, with the circular rotation velocity at the solar distance being V_0=227+/-23 km/s. The following principal semiaxes of the residual velocity dispersion ellipsoid have been found: (sigma1, sigma2, sigma3) = (47, 41, 29) km/s from a sample of young protoplanetary nebulae (with luminosities higher than 5000 Lo), (sigma1, sigma2, sigma3) = (50, 38, 28) km/s from a sample of older protoplanetary nebulae (with luminosities of 4000 Lo or 3500 Lo), and (sigma1, sigma_2, sigma3) = (91, 49, 36) km/s from a sample of halo nebulae (with luminosities of 1700 Lo)., 18 pages, 4 figures, 2 tabkes

Based on published data, we have produced a sample of planetary nebulae (PNe) that is complete within 2 kpc of the Sun. We have estimated the total number of PNe in the Galaxy from this sample to be 17000+/-3000 and determined the vertical scale height of the thin disk based on an exponential density distribution to be 197+/-10 pc. The next sample includes PNe from the Stanghellini-Haywood catalog with minor additions. For this purpose, we have used about 200 PNe with Peimbert's types I, II, and III. In this case, we have obtained a considerably higher value of the vertical scale height that increases noticeably with sample radius. We have experimentally found that it is necessary to reduce the distance scale of this catalog approximately by 20%. Then, for example, for PNe with heliocentric distances less than 4 kpc the vertical scale height is 256+/-12 kpc. A kinematic analysis has confirmed the necessity of such a reduction of the distance scale., 16 pqges, 6 figures, 2 tables

We have determined the Galactic rotation parameters and the solar Galactocentric distance R0 by simultaneously solving Bottlinger’s kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 73 masers spanning the range of Galactocentric distances from 3 to 14 kpc. The solutions found are Ω0 = 28.86 ± 0.45 km s−1 kpc−1, Ω′0 = −3.96 ± 0.09 km s−1 kpc−2, Ω″0 = 0.790 ± 0.027 km s−1 kpc−3, and R0 = 8.3 ± 0.2 kpc. In this case, the linear rotation velocity at the solar distance R0 is V = 241 ± 7 km s−1. Note that we have obtained the R0 estimate, which is of greatest interest, from masers for the first time; it is in good agreement with the most recent estimates and even surpasses them in accuracy.

To estimate the pitch angle i of the Galactic spiral arms, we have used data on Galactic masers with known trigonometric parallaxes. These masers are associated with very young objects located in active star-forming regions. The well-knownmethod of analyzing the “position angle-distance logarithm” diagram has been applied. Our estimates of the angle i obtained from four segments of different arms belonging to the grand-design structure are in satisfactory agreement between themselves and are close to i = −13°. The segment of the outer arm is of greatest interest. It contains only three masers, but we have additionally invoked data on 12 very young star clusters with their distances estimated by Camargo et al. from infrared photometry. Using such a combination of data, we have found i = −13.3° ± 1.3°. Comparison of this value with other spiral density wave parameters obtained from a kinematic analysis of masers leads us to conclude that the model of a four-armed spiral pattern is most likely realized in our Galaxy.

The Galactic orbits of 27 440 stars of all classes with accurate coordinates and parallaxes of more than 3 mas from the Hipparcos catalogue, proper motions from the Tycho-2 catalogue, and radial velocities from the Pulkovo Compilation of Radial Velocities (PCRV) are analyzed. The sample obtained is much more representative than the Geneva-Copenhagen survey and other studies of Galactic orbits in the solar neighborhood. An estimation of the influence of systematic errors in the velocities on orbital parameters shows that the errors of the proper motions due to the duplicity of stars are tangible only in the statistics of orbital parameters for very small samples, while the errors of the radial velocities are noticeable in the statistics of orbital parameters for halo stars. Therefore, previous studies of halo orbits may be erroneous. The distribution of stars in selection-free regions of the multidimensional space of orbital parameters, dereddened colors, and absolute magnitudes is considered. Owing to the large number of stars and the high accuracy of PCRV radial velocities, nonuniformities of this distribution (apart from the well-known dynamical streams) have been found. Stars with their peri- and apogalacticons in the disk, perigalacticons in the bulge and apogalacticons in the disk, perigalacticons in the bulge and apogalacticons in the halo, and perigalacticons in the disk and apogalacticons in the halo have been identified. Thus, the bulge and the halo are inhomogeneous structures, each consisting of at least two populations. The radius of the bulge has been determined as 2 kpc., Comment: 21 pages, 8 figures

Open star clusters from the MWSC (Milky Way Star Clusters) catalogue have been used to determine the Galactic rotation parameters. The circular rotation velocity of the solar neighborhood around the Galactic center has been found from data on more than 2000 clusters of various ages to be V_0=236+/-6 km s^{-1} for the adopted Galactocentric distance of the Sun R_0=8.3+/-0.2 kpc. The derived angular velocity parameters are \Omega_0=28.48+/-0.36 km s^{-1} kpc^{-1}, \Omega'_0=-3.50+/-0.08 km s^{-1} kpc^{-2}, and \Omega"_0= 0.331+/-0.037 km s^{-1} kpc^{-3}. The influence of the spiral density wave has been detected only in the sample of clusters younger than 50 Myr. For these clusters the amplitudes of the tangential and radial velocity perturbations are f_\theta=5.6+/-1.6 km s^{-1} and f_R=7.7+/-1.4 km s^{-1}, respectively; the perturbation wavelengths are \lambda_\theta=2.6+/-0.5 kpc (i_\theta=-11+/-2 degrees) and \lambda_R=2.1+/-0.5 kpc (i_R=-9+/-2 degrees) for the adopted four-armed model (m=4). The Sun's phase in the spiral density wave is (\chi_\odot)_\theta=-62+/-9 degrees and (\chi_\odot)_R =-85+/-10 degrees from the residual tangential and radial velocities, respectively., Comment: 18 pages, 5 figures

To study the peculiarities of the Galactic spiral density wave, we have analyzed the space velocities of Galactic Cepheids with proper motions from the Hipparcos catalog and line-of-sight velocities from various sources. First, based on the entire sample of 185 stars and taking $R_0 = 8$ kpc, we have found the components of the peculiar solar velocity $(u_\odot,v_\odot,w_\odot)=(7.6,11.6,6.1)\pm(0.8,1.1,0.6)$ km s$^{-1}$, the angular velocity of Galactic rotation $\Omega_0 = -27.4\pm0.6$ km s$^{-1}$ kpc$^{-1}$ and its derivatives $\Omega^{'}_0 = +4.07\pm0.21,$ km s$^{-1}$ kpc$^{-2}$ and $\Omega^{"}_0 = -0.83\pm0.17,$ km s$^{-1}$ kpc$^{-3}$, the amplitudes of the velocity perturbations in the spiral density wave $f_R=-6.7\pm0.7$ and $f_\theta= 3.5\pm0.5$ km s$^{-1}$, the pitch angle of a two-armed spiral pattern (m = 2) $i=-4.5\pm0.1^\circ$ (which corresponds to a wavelength $\lambda=2.0\pm0.1$ kpc), and the phase of the Sun in the spiral density wave $\chi_\odot=-191\pm5^\circ$. The phase $\chi_\odot$ has been found to change noticeably with the mean age of the sample. Having analyzed these phase shifts, we have determined the mean value of the angular velocity difference $\Omega_p-\Omega$, which depends significantly on the calibrations used to estimate the individual ages of Cepheids. When estimating the ages of Cepheids based on Efremov's calibration, we have found $|\Omega_p-\Omega_0|=9\pm2$ km s$^{-1}$ kpc$^{-1}$. The ratio of the radial component of the gravitational force produced by the spiral arms to the total gravitational force of the Galaxy has been estimated to be $f_{r0} = 0.04$., Comment: 17 pages, 5 figures, 2 tables

Based on data for 102 OB3 stars with known proper motions and radial velocities, we have tested the distances derived by Megier et al. from interstellar Ca II spectral lines. The internal reconciliation of the distance scales using the first derivative of the angular velocity of Galactic rotation Ω′0 and the external reconciliation with Humphreys’s distance scale for OB associations refined by Mel’nik and Dambis show that the initial distances should be reduced by ≈20%. Given this correction, the heliocentric distances of these stars lie within the range 0.6–2.6 kpc. A kinematic analysis of these stars at a fixed Galactocentric distance of the Sun, R0 = 8 kpc, has allowed the following parameters to be determined: (1) the solar peculiar velocity components (u⊙, v⊙, ω⊙) = (8.9, 10.3, 6.8) ± (0.6, 1.0, 0.4) km s−1; (2) the Galactic rotation parameters Ω0 = −31.5 ± 0.9 km s−1 kpc−1, Ω′0 = +4.49 ± 0.12 km s−1 kpc−2, Ω″0 = −1.05 ± 0.38 km s−1 kpc−3 (the corresponding Oort constants are A = 17.9 ± 0.5 km s−1 kpc−1, B = −13.6 ± 1.0 km s−1 kpc−1 and the circular rotation velocity of the solar neighborhood is |V0| = 252 ± 14 km s−1); (3) the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, fR = −12.5±1.1 km s−1 and fϑ = 2.0 ± 1.6 km s−1; the pitch angle for the two-armed spiral pattern i = −5.3° ± 0.3°, with the wavelength of the spiral density wave at the solar distance being λ = 2.3 ± 0.2 kpc; the Sun’s phase in the spiral wave x⊙ = −91° ± 4°.

The photometry from 2MASS, UCAC3 and SuperCosmos catalogues together with the proper motions from the Tycho-2, XPM and UCAC3 catalogues are used to select the all-sky samples of 34 white dwarfs, 1996 evolved and 7769 unevolved subdwarfs candidates for R from 9 to 17 magnitude. The samples are separated from the main sequence with admixture less than 10% owing to the detailed analysis of the distribution of the stars in the different color index (CI) vs. reduced proper motion (RPM) diagrams for various latitudes with special attention to the estimation of admixtures in the samples and with Monte-Carlo simulation. It is shown that the XPM and UCAC3 have the same level of proper motion accuracy. Most of the selected stars has at least 6-band photometry with accuracy is proved to be better than 0.2. The multicolor photometry allows us to eliminate some admixtures and reveal some binaries. The empirical calibrations of absolute magnitude versus CI and RPM for Hipparcos stars give us photometric distances and 3D distribution for all the stars. Although the selection method and uneven distribution of the XPM and UCAC3 data provide noticeable biases the preliminary conclusions are made. The subdwarfs show some concentration to the galactic centre hemisphere with voids because of extinction in the Gould belt and galactic plane. Some yet unexplained overdensities of the evolved subdwarfs are seen in several parts of the sky. For 183 stars with radial velocities 3D motion and galactic orbits are calculated. For 56 stars with Fe/H collected from various sources we find the relations of the metallicity with CI, asymmetric drift velocity and orbital eccentricity. It is shown that most unevolved subdwarfs belong to the halo with

Spatial velocities of all currently known 28 masers having trigonometric parallaxes, proper motion and line-of-site velocities are reanalyzed using Bottlinger's equations. These masers are associated with 25 active star-forming regions and are located in the range of galactocentric distances 3

The absolute proper motions of about 275 million stars from the Kharkov XPM catalog have been obtained by comparing their positions in the 2MASS and USNO--A2.0 catalogs with an epoch difference of about 45 yr for northern-hemisphere stars and about 17 yr for southern-hemisphere stars. The zero point of the system of absolute proper motions has been determined using 1.45 million galaxies. The equatorial components of the residual rotation vector of the ICRS/UCAC2 coordinate system relative to the system of extragalactic sources have been determined by comparing the XPM and UCAC2 stellar proper motions: ��_{x,y,z}=(-0.06,0.17,-0.84)+/-(0.15,0.14,0.14) mas yr^{-1}. These parameters have been calculated using about 1 million faintest UCAC2 stars with magnitudes R_{UCAC2}>16^m and J>14^m.7,for which the color and magnitude equation effects are negligible., 11 pages, 1 table, 5 figures

Based on a new version of the Hipparcos catalogue and an updated Geneva-Copenhagen survey of F and G dwarfs, we analyze the space velocity field of about 17000 single stars in the solar neighborhood. The main known clumps, streams, and branches (Pleiades, Hyades, Sirius, Coma Berenices, Hercules, Wolf 630-alpha Ceti, and Arcturus) have been identified using various approaches. The evolution of the space velocity field for F and G dwarfs has been traced as a function of the stellar age. We have managed to confirm the existence of the recently discovered KFR08 stream. We have found 19 Hipparcos stars, candidates for membership in the KFR08 stream, and obtained an isochrone age estimate for the stream, 13 Gyr. The mean stellar ages of the Wolf 630-alpha Ceti and Hercules streams are shown to be comparable, 4--6 Gyr. No significant differences in the metallicities of stars belonging to these streams have been found. This is an argument for the hypothesis that these streams owe their origin to a common mechanism., Comment: 23 pages, 9 figures

Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633 red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc. Using 3632 RGC stars with known proper motions, radial velocities, and photometric distances, we show that, apart from the star centroid velocity components relative to the Sun, only the model parameters that describe the stellar motions in the XY plane differ significantly from zero. We have studied the contraction (a negative K-effect) of the system of RGC stars as a function of their heliocentric distance and elevation above the Galactic plane. For a sample of distant (500--1000 pc) RGC stars located near the Galactic plane (|Z|=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the Galactic X axis directed toward the Galactic center with an angular velocity of -2.5+-0.3 km/s/kpc, which we associate with the warp of the Galactic stellar-gaseous disk., 23 pages, 7 figures, 4 tables

A fine structure related to the kinematic peculiarities of three components of the Scorpius-Centaurus association (LCC, UCL, and US) has been revealed in the UV-velocity distribution of Gould Belt stars. We have been able to identify the most likely members of these groups by applying the method of analyzing the two-dimensional probability density function of stellar UV velocities that we developed. A kinematic analysis of the identified structural components has shown that, in general, the center--of--mass motion of the LCC, UCL, and US groups follows the motion characteristic of the Gould Belt, notably its expansion. The entire Scorpius-Centaurus complex is shown to possess a proper expansion with an angular velocity parameter of 46+-8 km/s/kpc for the kinematic center with lo=-40 degrees and Ro=110 pc found. Based on this velocity, we have estimated the characteristic expansion time of the complex to be 21+-4 Myr. The proper rotation velocity of the Scorpius-Centaurus complex is lower in magnitude, is determined less reliably, and depends markedly on the data quality., Comment: 21 pages, 7 figures

We have obtained new estimates of the Sun's distance from the symmetry plane Zo and the vertical disk scale height h using currently available data on stellar OB associations, Wolf-Rayet stars, HII regions, and Cepheids. Based on individual determinations, we have calculated the mean Zo=-16+/-2 pc. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h = 40.2+/-2.1 pc from OB associations, h = 47.8+/-3.9 pc from Wolf-Rayet stars, h=48.4+/-2.5 pc from HII regions, and h = 66.2+/-1.6 pc from Cepheids. We have estimated the surface, \sum=6 kpc^{-2}, and volume, D(Zo) = 50.6 kpc^{-3}, densities from a sample of OB associations. We have found that there could be approximately 5000 OB associations in the Galaxy., 13 pages, 2 figures, 2 tables

We have shown previously (Bobylev et al 2011) that some of the stars in the Solar neighborhood today may have originated in the same star cluster as the Sun, and could thus be called Solar Siblings. In this work we investigate the sensitivity of this result to Galactic models and to parameters of these models, and also extend the sample of orbits. There are a number of good candidates for the Sibling category, but due to the long period of orbit evolution since the break-up of the birth cluster of the Sun, one can only attach probabilities of membership. We find that up to 10% (but more likely around 1 %) of the members of the Sun's birth cluster could be still found within 100 pc from the Sun today., 15 pages, 4 tables, 3 figures. Celestial Mechanics and Dynamical Astronomy (2014CeMDA.tmp...56V). arXiv admin note: text overlap with arXiv:1106.5632

We consider stars with radial velocities, proper motions, and distance estimates from the RAVE4 catalogue. Based on a sample of more than 145000 stars at distances $r, Comment: 13 pages,3 figures, 3 tables

Based on masers with measured trigonometric parallaxes, we have redetermined the spatial orientation parameters of the Local (Orion) arm. Using 23 sources (the Gould Belt objects were excluded), we have found that their spatial distribution can be approximated by a very narrow ellipsoid elongated in the direction L_1=77.1+/-2.9^o whose symmetry plane is inclined to the Galactic plane at an angle of 5.6+/-0.2^o. The longitude of the ascending node of the symmetry plane is l_\Omega=70+/-3^o. A new estimate for the pitch angle of the Local spiral arm has been obtained by an independent method: i=12.9+/-2.9^o. Previously, a belt of young B stars, the de Vaucouleurs.Dolidze belt, was pointed out on the celestial sphere with parameters close to such an orientation. We have refined the spatial orientation parameters of this belt based on a homogeneous sample of protostars. The de Vaucouleurs.Dolidze belt can be identified with the Local arm, with the belt proper as a continuous band on the celestial sphere like the Gould Belt being absent due to the peculiarities of the spatial orientation of the Local arm. Using the entire sample of 119 Galactic masers, we have shown that the third axis of their position ellipsoid has no deviation from the direction to the Galactic pole: B_3=89.7+/-0.1^o., Comment: 14 pages, 5 figures

Based on data on Galactic masers with measured trigonometric parallaxes, we have tested a nonlinear model of Galactic rotation using generalized Oort formulas. This model is shown to yield pretty good results up to heliocentric distances of 3--4 kpc. The main feature of the method is the possibility of estimating the solar Galactocentric distance Ro. This distance has been found by analyzing approximately 60 masers to be Ro=8.3+/-0.4 kpc. Our study of the three-dimensional kinematics of more than 100 masers based on the Ogorodnikov--Milne model has shown that significant nonlinearities are present only in the xy plane (rotation around the Galactic z axis) due to the peculiarities of the Galactic rotation curve. No significant linear dependences have been found in the xz and yz planes. We show the presence of a wave in the velocities w as a function of coordinate x or distance R with a wavelength of 3 kpc and an amplitude of 10 km/s. The wave is particularly prominent in the Local and Perseus arms., Comment: 14 pages, 6 figures. arXiv admin note: text overlap with arXiv:1406.0699

A new method for selecting stars in the Galactic bar based on 2MASS infrared photometry in combination with stellar proper motions from the Kharkiv XPM catalogue has been implemented. In accordance with this method, red clump and red giant branch stars are preselected on the color -- magnitude diagram and their photometric distances are calculated. Since the stellar proper motions are indicators of a larger velocity dispersion toward the bar and the spiral arms compared to the stars with circular orbits, applying the constraints on the proper motions of the preselected stars that take into account the Galactic rotation has allowed the background stars to be eliminated. Based on a joint analysis of the velocities of the selected stars and their distribution on the Galactic plane, we have confidently identified the segment of the Galactic bar nearest to the Sun with an orientation of 20$^\circ$--25$^\circ$ with respect to the Galactic center -- Sun direction and a semimajor axis of no more than 3 kpc., Comment: 14 pages, 7 figures

From the XHIP catalogue, we have selected 1872 F-G-K stars with relative parallax measurement errors, 11 pages, 1 table, 3 figures

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, $\Delta V_{\theta}$, and radial, $\Delta V_R,$ 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 $f_\theta=7.0\pm1.2$ km s$^{-1}$ and $f_R=7.8\pm0.7$ km s$^{-1}$, respectively, the perturbation wavelength is $\lambda=2.3\pm0.4$ 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 $\chi_\odot$ in the spiral density wave is $-50^\circ\pm15^\circ$ and $-160^\circ\pm15^\circ$ from the residual tangential and radial velocities, respectively., Comment: 14 pages, 3 figures, 2 tables

Based on published sources, we have created a kinematic database on 220 massive (>10 solar masses) young Galactic star systems located within, Comment: 25 pages, 9 figures, 3 tables

Maximum entropy signal processing for complex signal reconstruction may be placed within a MAP (maximum a posteriori) framework. This permits injection into the algorithm of prior information in the form of a cross-reference function and a noise-rejection term. Simulated complex images are well-reconstructed by the procedure.

The XPM-1.0 is the regular version of the XPM catalogue. In comparison with XPM the astrometric catalogue of about 280 millions stars covering entire sky from -90 to +90 degrees in declination and in the magnitude range 10^m

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., Comment: 12 pages, 2 tables, 6 figures

The Maximum Entropy Method is widely used for reconstruction of real non-negative functions, such as images (intensity distributions) in optics and astronomy. The problem of reconstruction exists not only for real non-negative functions: in radio holography, for example, it is often necessary to reconstruct a coherent source field distribution described by a complex function. In this paper the Generalization of Maximum Entropy Method for reconstruction of functions of different types (real non-negative as well as real with alternating signs and complex ones) is suggested. Though this problem is considered for two-dimensional functions it is evident that the generalization obtained can be applied for functions of different dimensions. Numerical simulation results show high quality of reconstruction of complex functions and stability of the algorithm in the presence of measurement errors.

The dedicated “QUASAR” Very Long Baseline Network is presented. Principal Network characteristics are given.

We analyze the encounters of the neutron star (pulsar) Geminga with open star clusters in the OB association OriOB1a through the integration of epicyclic orbits into the past by taking into account the errors in the data. The open cluster ASCC21 is shown to be the most probable birthplace of either a single progenitor star for the Geminga pulsar or a binary progenitor system that subsequently broke up. Monte Carlo simulations of Geminga--ASCC21 encounters with the pulsar radial velocity Vr =-100+-50 km/s have shown that close encounters could occur between them within, 14 pages, 5 figures

A new multi-frequency synthesis algorithm for reconstructing images from multi-frequency VLBI data is proposed. The algorithm is based on a generalized maximum-entropy method, and makes it possible to derive an effective spectral correction for images over a broad frequency bandwidth, while simultaneously reconstructing the spectral-index distribution over the source. The results of numerical simulations demonstrating the capabilities of the algorithm are presented., 17 pages, 8 figures

Based on currently available data on the three-dimensional field of space velocities of young (, Comment: 21 pages, 8 figures