arXiv subjects

V. V. Bobylev

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

At least 91 records · Page 5Linked to original sources

arXiv2015

Residual HCRF Rotation relative to the Inertial Coordinate System

VLBI measurements of the absolute proper motions of 23 radio stars have been collected from published data. These are stars with maser emission, or very young stars, or asymptotic-giant-branch stars. By comparing these measurements with the stellar proper motions from the optical catalogs of the Hipparcos Celestial Reference Frame (HCRF), we have found the components of the residual rotation vector of this frame relative to the inertial coordinate system: (ω_x,ω_y,ω_z) = (-0.39,-0.51,-1.25)+/-(0.58,0.57,0.56) mas/yr. Based on all the available data, we have determined new values of the components of the residual rotation vector for the optical realization of the HCRF relative to the inertial coordinate system: (ω_x,ω_y,ω_z) = (-0.15,+0.24,-0.53)+/-(0.11,0.10,0.13) mas/yr.

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arXiv2015

Probabilities for Solar Siblings

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.

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arXiv2014

Determination of the Solar Galactocentric distance from masers kinemics

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 Ω_0 = 29.7+/-0.5 km s^{-1} kpc^{-1}, Ω'_0 = -4.20+/-0.11 km s^{-1} kpc^{-2}, Ω"_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}.

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arXiv2014

A new estimate of the Local Standard of Rest from data on young Galactic objects

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 χ_o in the spiral density wave.

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arXiv2014

The Gould Belt, the de Vaucouleurs-Dolidze Belt, and the Orion Arm

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_Ω=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.

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arXiv2014

Analysis of Galactic Rotation from Masers based on a Nonlinear Oort Model

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.

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arXiv2014

Detection of periodic variations in vertical velocities of Galactic masers

We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of VLBI. We have obtained series of residual tangential, ΔV_{circ}, and radial, ΔV_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_θ=6.0+/-2.6 km/s and f_R=7.2+/-2.2 km/s, respectively; the perturbation wavelengths are λ_θ=3.2+/-0.5 kpc and λ_R=3.0+/-0.6 kpc for a four-armed spiral model, m=4. The phase of the Sun χ_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 λ_W=3.4+/-0.7 kpc and the amplitude f_W=4.3+/-1.2 km/s.

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arXiv2014

Determination of Galactic Rotation Parameters and the Solar Galactocentric Distance Ro from 73 Masers

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.

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arXiv2014

Search for Kinematic Siblings of the Sun Based on Data from the XHIP Catalog

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.

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arXiv2014

Elemental Abundances of Solar Sibling Candidates

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.

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arXiv2014

Investigation of the Galactic Bar based on Photometry and Stellar Proper Motions

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.

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arXiv2013

Galactic Kinematics from a Sample of Young Massive Stars

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_θ=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_θ=2.9+/-2.1 km/s and χ_\odot=-104+/-6 deg.

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arXiv2013

Kinematics of nearby OB3 stars with interstellar CaII line distances

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 $λ\approx2.3$ kpc and phase of the Sun in spiral wave $χ_\odot\approx-90^\circ$. 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.

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arXiv2013

Re-determining the Galactic spiral density wave parameters from data on masers with trigonometric parallaxes

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 $θ$ 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 $λ=2.4 \pm 0.4$ 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 $χ_\odot=-160 \pm 15^\circ$, and the pitch angle of $-5.5 \pm 1^\circ$.

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arXiv2013

Corrections for the Lutz-Kelker Bias for Galactic Masers

Based on published data, we have collected information about Galactic maser sources with measured distances. In particular, 44 Galactic maser sources located in star-forming regions have trigonometric parallaxes, proper motions, and radial velocities. In addition, ten more radio sources with incomplete information are known, but their parallaxes have been measured with a high accuracy. For all 54 sources, we have calculated the corrections for the well-known Lutz-Kelker bias. Based on a sample of 44 sources, we have refined the parameters of the Galactic rotation curve. Thus, at R_0=8 kpc, the peculiar velocity components for the Sun are (Uo,Vo,Wo)=(7.5,17.6,8.4)+\-(1.2,1.2,1.2) km s^-1 and the angular velocity components are ω_0=-28.7+\-0.5 km s^-1 kpc^-1, ω'_0=+4.17+\-0.10 km s^-1 kpc^-2, and ω''_0=-0.87+\-0.06 km s^-1 kpc^-3. The corresponding Oort constants are A=16.7+\-0.6 km s^-1 kpc^-1 and B=-12.0+\-1.0 km s^-1 kpc^-1; the circular rotation velocity of the solar neighborhood around the Galactic center is V_0 = 230+\-16 km s^-1. We have found that the corrections for the Lutz-Kelker bias affect the determination of the angular velocity ω_0 most strongly; their effect on the remaining parameters is statistically insignificant. Within the model of a two-armed spiral pattern, we have determined the pattern pitch angle i=-6.5^\circ and the phase of the Sun in the spiral wave χ_0=150^\circ.

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arXiv2012

Estimation of the SolarGalactocentric Distance and Rotation Velocity from Near-Solar-Circle Objects

We have tested the method of determining the solar Galactocentric distance R_0 and Galactic rotation velocity $V_0$ modified by Sofue et al. using near-solar-circle objects. The motion of objects relative to the local standard of rest has been properly taken into account. We show that when such young objects as star-forming regions or Cepheids are analyzed, allowance for the perturbations produced by the Galactic spiral density wave improves the statistical significance of the estimates. The estimate of R_0=7.25\pm0.32 kpc has been obtained from 19 star-forming regions. The following estimates have been obtained from a sample of 14 Cepheids (with pulsation periods P>5^d): R_0=7.66\pm0.36 kpc and V_0=267\pm 17 km s^{-1}. We consider the influence of the adopted Oort constant A and the character of stellar proper motions (Hipparcos or UCAC4). The following estimates have been obtained from a sample of 18 Cepheids with stellar proper motions from the UCAC4 catalog: R_0=7.64\pm0.32 kpc and V_0=217\pm 11 km s^{-1}.

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arXiv2012

Estimation of the Galactic Spiral Pattern Speed from Cepheids

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 $Ω_0 = -27.4\pm0.6$ km s$^{-1}$ kpc$^{-1}$ and its derivatives $Ω^{'}_0 = +4.07\pm0.21,$ km s$^{-1}$ kpc$^{-2}$ and $Ω^{"}_0 = -0.83\pm0.17,$ km s$^{-1}$ kpc$^{-3}$, the amplitudes of the velocity perturbations in the spiral density wave $f_R=-6.7\pm0.7$ and $f_θ= 3.5\pm0.5$ 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 $λ=2.0\pm0.1$ kpc), and the phase of the Sun in the spiral density wave $χ_\odot=-191\pm5^\circ$. The phase $χ_\odot$ 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 $Ω_p-Ω$, 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 $|Ω_p-Ω_0|=9\pm2$ 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 $f_{r0} = 0.04$.

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arXiv2012

Redetermination of Galactic Spiral Density Wave Parameters Based on Spectral Analysis of Maser Radial Velocities

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 $(3.5<R<13.2$ kpc) and are characterized by a wide scatter of position angles $θ$ in the Galactic XY plane. This has required an accurate allowance for the dependence of the perturbation phase both on the logarithm of the Galactocentric distances and on the position angles of the objects. To increase the significance of the extraction of periodicities from data series with large gaps, we have proposed and implemented a spectrum reconstruction method based on a generalized maximum entropy method. As a result, we have extracted a periodicity describing a spiral density wave with the following parameters from the maser radial velocities: the perturbation amplitude $f_R = 7.7^{+1.7}_{-1.5}$ km s$^{-1}$, the perturbation wavelength $λ=2.2^{+0.4}_{-0.1}$ kpc, the pitch angle of the spiral density wave $i=-5^{+0.2^\circ}_{-0.9^\circ}$, and the phase of the Sun in the spiral density wave $χ_\odot= -147^{+3^\circ}_{-17^\circ}$.

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