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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

The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). Three GCs (NGC 6341, NGC 7078, and $\omega$ Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20\% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt., Comment: 14 pages, 5 figures, 3 tables

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 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<-150 km/s). The stars of the BB17-1 and BB17-2 clumps are associated with the kinematic groups VelHel-6 and VelHel-7 detected previously by Helmi et al. We give the greatest attention to the BB17-3 clump. The latter is shown to be most closely linked with the debris of the globular cluster \omega Cen. In the BB17-3 clump we have identified 28 stars with a low velocity dispersion with respect to the center of their distribution. All these stars have very close individual age estimates: \log t\approx 10. The distribution of metallicity indices in this sample is typical for the stars of the globular cluster \omega Cen. In our opinion, the BB17-3 clump can be described as a homogeneous stream in the debris of the cluster \omega Cen., Comment: 12 pages, 4 figures, 1 table

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

The spatial velocities of the stars with high-precision positions, proper motions and parallaxes from the Gaia TGAS catalog and line-of-sight velocities from the RAVE5 catalog are considered. From the sample of 92395 stars with the age estimates we have obtained the following kinematic parameters: (U,V,W)=(9.42,20.34,7.21)+/-0.12,0.10,0.09) km/s, \Omega=26.29+/-0.39 km/s/kpc and \Omega'=-3.89+/-0.08 km/s/kpc^2, where V0=210+/-6 km/s (for adopted R0=8.0+/-0.2 kpc), and the Oort constants A=15.57+/-0.31 km/s/kpc and B=-10.72+/-0.50 km/s/kpc. It is shown that the parameters \Omega and \Omega' are stable to the star age. A comparative analysis of the Bottlinger model parameters obtained separately from the RAVE5 catalog line-of-sight velocities and the Gaia TGAS, UCAC4 and PPMXL catalogs proper motion has been made. It is shown that these parameters are in good agreement with each other when derived from the proper motions of both the terrestrial catalogs and catalog Gaia TGAS. At the same time, it was established that the values of the Bottlinger model parameters obtained from the line-of-sight velocities can differ from the corresponding parameters obtained from the proper motions. The reduction of the line-of-sight velocities from the RAVE5 catalog is proposed for eliminating these differences., Comment: 19 pages, 4 figures, 7 tables

High-accuracy absolute proper motions, radial velocities, and distances have now been measured for a number of dwarf-galaxy companions of the Milky Way, making it possible to study their 3D dynamics. Galactic orbits for 11 such galaxies (Fornax, Sagittarius, Ursa Minor, LMC, SMC, Sculptor, Sextans, Carina, Draco, Leo I, Leo II) have been derived using two previously refined models for the Galactic potential with the Navarro-Frenk-White and Allen-Santill'an expressions for the potential of the dark-matter halo, and two different masses for the Galaxy within 200 kpc - 0.75x10^12 Mo and 1.45x10^12 Mo. The character of the orbits of most of these galaxies indicates that they are tightly gravitationally bound to the Milky Way, even with the lower-mass model for the gravitational potential. One exception is the most distant galaxy in the list, Leo I, whose orbit demonstrates that it is only weakly gravitationally bound, even using the higher-mass model of the gravitational potential., Comment: 15 pages, 6 figures, 5 tables

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., Comment: 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)., Comment: 18 pages, 4 figures, 2 tabkes

Galactic orbits have been constructed over long time intervals for ten globular clusters located near the Galactic center. A model with an axially symmetric gravitational potential for the Galaxy was initially applied, after which a non-axially symmetric potential corresponding to the central bar was added. Variations in the trajectories of all these globular clusters in the XY plane due to the influence of the bar were detected. These were greatest for the cluster Terzan 4 in the meridional (RZ) plane. The globular clusters Terzan 1, Terzan 2, Terzan 4, Terzan 9, NGC 6522, and NGC 6558 always remained within the Galactic bulge, no farther than 4 kpc from the Galactic center., Comment: 11 pages, 5 tables, 2 figures

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., Comment: 16 pqges, 6 figures, 2 tables

This paper is a continuation of our recent paper devoted to refining the parameters of three component (bulge, disk, halo) axisymmetric model Galactic gravitational potentials differing by the expression for the dark matter halo using the velocities of distant objects. In all models the bulge and disk potentials are described by the Miyamoto-Nagai expressions. In our previous paper we used the Allen-Santill'an (I), Wilkinson--Evans (II), and Navarro-Frenk-White (III) models to describe the halo. In this paper we use a spherical logarithmic Binney potential (model IV), a Plummer sphere (model V), and a Hernquist potential (model VI) 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 the listed models, which are employed most commonly at present. The model rotation curves are fitted to the observed velocities by taking into account the constraints on the local matter density and the vertical force . Model VI looks best among the three models considered here from the viewpoint of the achieved accuracy of fitting the model rotation curves to the measurements. This model is close to the Navarro-Frenk-White model III refined and considered best in our previous paper, which is shown using the integration of the orbits of two globular clusters, Lynga 7 and NGC 5053, as an example., Comment: 14 pages, 3 figures, 3 tables. arXiv admin note: substantial text overlap with arXiv:1607.08050

We consider two previously studied samples of OB stars with different distance scales. The first one consists of 98 massive spectroscopic binary stars with photometric distances, and the second one consists on 140 OB stars with the distances determined along the lines of interstellar calcium. The OB stars are located at distances up to 7 kpc from the Sun. They are identified with the Gaia DR1 catalog. It is shown that the use of the proper motions, taken from the Gaia DR1 catalog, allows to reduce random errors of determination of the Galactic rotation parameters in comparison with the previously known ones. From the analysis of 208 OB stars from the Gaia DR1 catalog with proper motions and parallaxes with relative errors less than 200% we found the Galactic kinematic parameters. In addition the Galactic rotation parameters were obtained from only line-of-sight velocities of the same stars. From the comparison of the two values of \Omega^{'}_0 a distance scale of the Gaia DR1 catalog was determined as a value close to unit, namely 0.96. From 238 OB-stars of the united sample with photometric distances for stars of the first sample and distances in the calcium scale for stars of the second sample, line-of-sight velocities and proper motions from the Gaia DR1 catalog, were found the following kinematic parameters: (U,V,W)_\odot=(8.19,9.28,8.79)+/-(0.74,0.92,0.74) km/s, \Omega_0=31.53+/-0.54 km/s/kpc, \Omega^{'}_0=-4.44+/-0.12 km/s/kpc^2, \Omega^{"}_0=0.706+/-0.100 km/s/kpc^3, here Oort constants: A=-17.77+/-0.46 km/s/kpc, B=13.76+/-0.71 km/s/kpc and V_0=252+/-8 km/s., Comment: 12 pages, 3 figures, accepted for publication in Astronomy Letters (2017, Issue 3). arXiv admin note: text overlap with arXiv:1507.08049

We have identified the four most significant features in the UV velocity distribution of solar neighborhood stars: H1,H2 and W1,W2 in the Hercules and Wolf 630 streams respectively. We have put the task of determining number of characteristics of the central Galactic bar independently from each of the identified features by assuming that the Hercules and Wolf 630 streams have 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 \Omega_b lies within the range 45-52 km/s/kpc with a mean of 48.1+/-1.0 km/s/kpc, while the bar angle \theta_b is within the range 35-65 degrees with a mean of 50+/-4 degrees. The results obtained are consistent with the view that the Hercules and Wolf 630 streams could be formed by a single mechanism associated with the fact that a long-term influence of the Galactic bar led to a characteristic bimodal splitting of the UV velocity plane., Comment: 9 pages, 3 figures, accepted for publication in Baltic Astronomy. arXiv admin note: substantial text overlap with arXiv:1603.00610

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

We have collected literature data on young Galactic objects such as masers with VLBI-measured trigonometric parallaxes, OB associations, HII regions and Cepheids. We have recently established that vertical disk scale height is strongly influenced by the objects of the Local arm. In the present work we used samples that do not contain objects in this arm. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h=46+/-5 pc from 69 masers with trigonometric parallaxes, h=36+/-3 pc from 59 OB associations, h=35.6+/-2.7 pc from 147 HII regions, h=52.1+/-1.9 pc from 195 young Cepheids, and h=72.0+/-2.3 pc from 192 old Cepheids., Comment: 6 pages, 3 figures, accepted to Baltic Astronomy

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 \rho_\odotand the force K_{z=1.1} acting perpendicularly to the Galactic plane. The Galactic mass within a sphere of radius 50 kpc, M_G (R<=50 kpc)=(0.41+/-0.12)x10^12 M_\odot, is shown to satisfy all three models. The differences between the models become increasingly significant with increasing radius R. In model I, the Galactic mass within a sphere of radius 200 kpc turns out to be greatest among the models considered, M_G (R<=200 kpc)=(1.45+/-0.30)x10^12 M_\odot, and the smallest value has been found in model II, M_G (R<=200 kpc)=(0.61+/-0.12)x10^{12} M_\odot. In our view, model III is the best one among those considered, because it ensures the smallest residual between the data and the constructed model rotation curve provided that the constraints on the local parameters hold with a high accuracy. Here, the Galactic mass is M_G (R<=200 kpc)=(0.75+/-0.19)x10^12 M_\odot. A comparative analysis with the models by Irrgang et al. (2013), including those using the integration of orbits for the two globular clusters NGC 104 and NGC 1851 as an example, has been performed. The third model is shown to have subjected to a significant improvement., Comment: 22 pages, 7 figures, 2 tables

We applied the currently most comprehensive version of the statistical-parallax technique to derive kinematical parameters of the maser sample with 136 sources. Our kinematic model comprises the overall rotation of the Galactic disk and the spiral density-wave effects. We take into account the variation of radial velocity dispersion with Galactocentric distance. The best description of the velocity field is provided by the model with constant radial and vertical velocity dispersions, $(\sigma U0, \sigma W0) \approx (9.4 \pm 0.9~, 5.9 \pm 0.8)~ km/s$. We compute flat Galactic rotation curve over the Galactocentric distance interval from 3 to 15 kpc and find the local circular rotation velocity to be $ V_0 \approx (235-238)$~ km/s $\pm 7$~ km/s. We also determine the parameters of the four-armed spiral pattern (pitch angle $i \approx (-10.4 \pm 0.3)^\circ$ and the phase of the Sun $\chi_0 \approx (125 \pm 10) ^\circ$). The radial and tangential spiral perturbations are about $f_R \approx (-6.9 \pm 1.4)$~km/s, $f_\Theta \approx (+2.8 \pm 1.0$) ~km/s. The kinematic data yield a solar Galactocentric distance of $R_0 \approx (8.24 \pm 0.12)~kpc$. Based on rotation curve parameters and the asymmetric drift we Infer the exponential disk scale $H_D \approx (2.7 \pm 0.2)$ ~kpc under assumption of marginal stability of the intermediate-age disk, and finally we estimate the minimum local surface disk density, $\Sigma (R_0) > (26 \pm 3) ~ M_\odot pc^{-2}$., Comment: 16 pages, 8 figures, 5 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

Data on HII regions, molecular clouds, and methanol masers have been used to estimate the Sun's distance from the symmetry plane zo and the vertical disk scale height h. Kinematic distance estimates are available for all objects in these samples. The Local-arm (Orion-arm) objects are shown to affect noticeably the pattern of the z distribution. The deviations from the distribution symmetry are particularly pronounced for the sample of masers with measured trigonometric parallaxes, where the fraction of Local-arm masers is large. The situation with the sample of HII regions in the solar neighborhood is similar. We have concluded that it is better to exclude the Local arm from consideration. Based on the model of a self-gravitating isothermal disk, we have obtained the following estimates from objects located in the inner region of the Galaxy (R<= Ro): zo= -5.7+/-0.5 pc and h2=24.1+/-0.9 pc from the sample of 639 methanol masers, zo=-7.6+/-0.4 pc and h2=28.6+/-0.5 pc from 878 HII regions, zo=-10.1+/-0.5 pc and h2=28.2+/-0.6 pc from 538 giant molecular clouds., Comment: 15 pages, 6 figures, 1 table

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 $r<0.5$~kpc, we have found the following kinematic parameters: (U,V,W)_\odot=(9.12, 20.80, 7.66)\pm(0.10, 0.10, 0.08) km s^{-1}, \Omega_0=28.71\pm0.63 km s^{-1} kpc^{-1}, and \Omega'_0=-4.28\pm0.11 km s^{-1} kpc^{-2}. This gives the linear rotation velocity V_0=230\pm12 km s^{-1} (for the adopted R_0= 8.0\pm0.4 kpc) and the Oort constants A=17.12\pm0.45 km s^{-1} kpc^{-1} and B=-11.60\pm0.77 km s^{-1} kpc^{-1}. The 2D velocity distributions in the UV, UW, and VW planes have been constructed using a local sample, r<0.25 kpc, consisting of \sim 47000 stars. A difference of the UV velocity distribution from the previously known ones constructed from a smaller amount of data has been revealed. It lies in the fact that our distribution has an extremely enhanced branch near the Wolf 630 peak. A previously unknown peak at (U,V)=(-96,-10) km s^{-1} and a separate new feature in the Wolf 630 stream, with the coordinates of its center being (U,V)=(30,-40) km s^{-1}, have been detected., Comment: 13 pages,3 figures, 3 tables

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., Comment: 13 pages, 2 figures, 2 tables

We consider three samples of O- and B-type stars from the solar neighborhood 0.6--4 kpc for which we have taken the distances, line-of-sight velocities, and proper motions from published sources. The first sample contains 120 massive spectroscopic binaries. O stars with spectroscopic distances from Patriarchi et al. constitute the second sample. The third sample consists of 168 OB3 stars whose distances have been determined from interstellar calcium lines. The angular velocity of Galactic rotation at the solar distance $\Omega_0,$ its two derivatives $\Omega'_0$ and $\Omega"_0,$ and the peculiar velocity components of the Sun $(U,V,W)_\odot$ are shown to be well determined from all three samples of stars. They are determined with the smallest errors from the sample of spectroscopic binary stars and the sample of stars with the calcium distance scale. The fine structure of the velocity field associated with the influence of the Galactic spiral density wave clearly manifests itself in the radial velocities of spectroscopic binary stars and in the sample of stars with the calcium distance scale., Comment: 21 pages, 9 figures, 1 table

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., Comment: 15 pages, 4 tables, 3 figures. Celestial Mechanics and Dynamical Astronomy (2014CeMDA.tmp...56V). arXiv admin note: text overlap with arXiv:1106.5632

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: (U_o,V_o,W_o)_{LSR}= (6.0,10.6,6.5)+/-(0.5,0.8,0.3) km s^{-1}. We have found that the Solar velocity components (U_o)_{LSR} and (V_o)_{LSR} are very sensitive to the Solar radial phase \chi_o in the spiral density wave., Comment: 11 pages, 1 figure, 3 tables. Paper was presented at the Conference "Modern Stellar Astronomy-2014" held in Rostov-on-Don State University on May 28-30. Accepted for publication in Baltic Astronomy

We have determined the Galactic rotation parameters and the solar Galactocentric distance $R_0$ 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 93 masers spanning the range of Galactocentric distances R from 3 to 15 kpc. The solutions found are \Omega_0 = 29.7+/-0.5 km s^{-1} kpc^{-1}, \Omega'_0 = -4.20+/-0.11 km s^{-1} kpc^{-2}, \Omega"_0 =0.730+/-0.029 km s^{-1} kpc^{-3}, and R_0=8.03+/-0.12 kpc. In this case, the linear rotation velocity at the solar distance R_0 is V_0=238+/-6 km s^{-1}., Comment: 8 pages, 2 figures, 1 table. Paper was presented at the Conference "Modern Stellar Astronomy-2014" held in Rostov-on-Don State University on May 28-30, 2014, accepted for pubication in Baltic Astronomy

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

We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of VLBI. We have obtained series of residual tangential, \Delta V_{circ}, and radial, \Delta V_R, velocities for 107 masers. Based on these series, we have re-determined parameters of the Galactic spiral density wave using the method of spectral (periodogram) analysis. The tangential and radial perturbation amplitudes are f_\theta=6.0+/-2.6 km/s and f_R=7.2+/-2.2 km/s, respectively; the perturbation wavelengths are \lambda_\theta=3.2+/-0.5 kpc and \lambda_R=3.0+/-0.6 kpc for a four-armed spiral model, m=4. The phase of the Sun \chi_0 in the spiral density wave is -79^\circ+/-14^\circ and -199^\circ+/-16^\circ from the residual tangential and radial velocities, respectively. The most interesting result of this work is detecting a wave in vertical spatial velocities W versus distance R from the Galactic rotation axis. From the spectral analysis, we have found the following characteristics of this wave: the perturbation wavelength is \lambda_W=3.4+/-0.7 kpc and the amplitude f_W=4.3+/-1.2 km/s., Comment: 5 pages, 4 figures, accepted by MNRAS Letters

We have determined the Galactic rotation parameters and the solar Galactocentric distance R_0 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 Omega_0 = 28.86 +/- 0.45 km/s/kpc, Omega'_0 = -3.96 +/- 0.09 km/s/kpc^2, Omega"_0 =0.790 +/- 0.027 km/s/kpc^3, and R_0=8.3 +/- 0.2 kpc.In this case, the linear rotation velocity at the solar distance Ro is V_0=241 +/- 7 km/s. Note that we have obtained the Ro 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., Comment: 12 pages, 2 figures

From the XHIP catalogue, we have selected 1872 F-G-K stars with relative parallax measurement errors <20% and absolute values of their space velocities relative to the Sun <15 km/s. For all these stars, we have constructed their Galactic orbits for 4.5 Gyr into the past using an axisymmetric Galactic potential model with allowance made for the perturbations from the spiral density wave. Parameters of the encounter with the solar orbit have been calculated for each orbit. We have detected three new stars whose Galactic orbits were close to the solar one during a long time interval in the past. These stars are HIP 43852, HIP 104047, and HIP 112158. The spectroscopic binary HIP 112158 is poorly suited for the role of a kinematic sibling of the Sun by its age and spectroscopic characteristics. For the single star HIP 43852 and the multiple system HIP 104047, this role is quite possible. We have also confirmed the status of our previously found candidates for close encounters, HIP 47399 and HIP 87382. The star HIP 87382 with a chemical composition very close to the solar one is currently the most likely candidate, because it persistently shows close encounters with the Sun on time scales of more than 3 Gyr when using various Galactic potential models both without and with allowance made for the influence of the spiral density wave., Comment: 11 pages, 1 table, 3 figures

Dynamical information along with survey data on metallicity and in some cases age have been used recently by some authors to search for candidates of stars that were born in the cluster where the Sun formed. We have acquired high resolution, high signal-to-noise ratio spectra for 30 of these objects to determine, using detailed elemental abundance analysis, if they could be true solar siblings. Only two of the candidates are found to have solar chemical composition. Updated modeling of the stars' past orbits in a realistic Galactic potential reveals that one of them, HD162826, satisfies both chemical and dynamical conditions for being a sibling of the Sun. Measurements of rare-element abundances for this star further confirm its solar composition, with the only possible exception of Sm. Analysis of long-term high-precision radial velocity data rules out the presence of hot Jupiters and confirms that this star is not in a binary system. We find that chemical tagging does not necessarily benefit from studying as many elements as possible, but instead from identifying and carefully measuring the abundances of those elements which show large star-to-star scatter at a given metallicity. Future searches employing data products from ongoing massive astrometric and spectroscopic surveys can be optimized by acknowledging this fact., Comment: ApJ, in press. Tables 2 and 4 are available in full in the "Other formats: source" download

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

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., Comment: 7 pages, 2 figures, 4 tables; accepted to MNRAS

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

Based on published sources, we have created a kinematic database on 220 massive (>10 solar masses) young Galactic star systems located within <3 kpc of the Sun. Out of them, approximately 100 objects are spectroscopic binary and multiple star systems whose components are massive OB stars; the remaining objects are massive Hipparcos B stars with parallax errors of no more than 10 percent. Based on the entire sample, we have constructed the Galactic rotation curve, determined the circular rotation velocity of the solar neighborhood around the Galactic center at Ro=8 kpc, Vo=259+-16 km/s, and obtained the following spiral density wave parameters: the amplitudes of the radial and azimuthal velocity perturbations f_R=-10.8+/-1.2 km/s, and f_\theta=7.9+/-1.3 km/s, respectively; the pitch angle for a two-armed spiral pattern i=-6.0+/-0.4 deg., with the wavelength of the spiral density wave near the Sun being 2.6+/-0.2 kpc; and the radial phase of the Sun in the spiral density wave -120+/-4 deg. We show that such peculiarities of the Gould Belt as the local expansion of the system, the velocity ellipsoid vertex deviation, and the significant additional rotation can be explained in terms of the density wave theory. All these effects decrease noticeably once the influence of the spiral density wave on the velocities of nearby stars has been taken into account. The influence of Gould Belt stars on the Galactic parameter estimates has also been revealed. Eliminating them from the kinematic equations has led to the following new values of the spiral density wave parameters: f_\theta=2.9+/-2.1 km/s and \chi_\odot=-104+/-6 deg., Comment: 25 pages, 9 figures, 3 tables

The parameters of the Galactic spiral wave are re-determined using a modified periodogram (spectral) analysis of the galactocentric radial velocities of 58 masers with known trigonometric parallaxes, proper motions, and line-of-site velocities. The masers span a wide range of galactocentric distances, $3<$R$<14$ kpc, which, combined with a large scatter of position angles $\theta$ of these objects in the Galactic plane XY, required an accurate account of logarithmic dependence of spiral-wave perturbations on both galactocentric distance and position angle. A periodic signal was detected corresponding to the spiral density wave with the wavelength $\lambda=2.4 \pm 0.4$ kpc, peak velocity of wave perturbations $f_R=7.5 \pm 1.5$ km s$^{-1}$, the phase of the Sun in the density wave $\chi_\odot=-160 \pm 15^\circ$, and the pitch angle of $-5.5 \pm 1^\circ$., Comment: 6 pages, 5 figures, 1 table. Astron. Nachrichten (submitted). arXiv admin note: text overlap with arXiv:1208.4565

We tested the distances derived from the equivalent widths of interstellar CaII spectral lines by Megier et al. 2009. To this end, we used a sample of nearby 126 young OB3 stars ($r<1$ kpc) with known proper motions and line-of-site velocities. It is shown that these stars are tightly bounded with the Gould Belt structure. Most part of this sample (about 100 stars) show the same kinematics as the sample of distant OB3 stars. Their galactocentric radial velocities are in good agreement with the following spiral density wave parameters: amplitude of radial perturbations $f_R\approx$12 km/s, wavelength $\lambda\approx2.3$ kpc and phase of the Sun in spiral wave $\chi_\odot\approx-90^\circ$. But we revealed 20 stars with absolutely unusual kinematical features. Their galactocentric radial velocities show a wave, biased on $\approx180^\circ$ with respect to the wave, found from the whole sample. The idea of superposition of two spiral patterns seems to be probable., Comment: 5 pages, 3 figures. Astron. Nachrichten (submitted)

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

The well-known phase problem which means image reconstruction from only spectrum magnitude without using any spectrum phase information is considered basically in application to VLBI mapping of compact extragalactic radio sources (active galactic nuclei). The method proposed for phaseless mapping is based on the reconstruction of the spectrum magnitude on the entire UV plane from the measured visibility magnitude on a limited set of points and the reconstruction of the sought-for image of the source by Fienup's error-reduction iterative algorithm from the spectrum magnitude reconstructed at the first stage. It is shown that the technique used ensures unique solution (within a class of equivalent functions) for AGNs with typical structure morphology "bright core + week jet". The method proposed can be used, for example, for imaging with ultra-high resolution using a space{ground radio interferometer with a space antenna in a very high orbit ("RadioAstron"). In this case, a multi-element interferometer essentially degenerates into a two-element interferometer and the degeneracy of the close-phase relations prevents the use of standard methods for hybrid mapping and self-calibration. The capabilities and restrictions of the method are demonstrated on a number of model experiments. For a few selected AGNs the images are obtained from VLBA observations., Comment: 21 pages, 19 figures, presented at IV Finnish-Russian Radio Astronomy Symposium, 15-18 October 2012, Lammi Biological Station, Finland

To redetermine the Galactic spiral density wave parameters, we have performed a spectral (Fourier) analysis of the radial velocities for 44 masers with known trigonometric parallaxes, proper motions, and line-of-sight velocities. The masers are distributed in a wide range of Galactocentric distances $(3.5

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., Comment: 17 pages, 9 figures

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., Comment: 11 pages, 12 figures, 6 tables. Accepted for publication in MNRAS, 2011

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., Comment: 13 pages, 7 figures. Accepted for publication in A&A, 2011

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

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: \omega_{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., Comment: 11 pages, 1 table, 5 figures