arXiv subjects

A. T. Bajkova

Publications and source records attributed to A. T. Bajkova.

At least 91 records · Page 5Linked to original sources

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.

astro-ph.SR↗

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 Orbits of Hipparcos Stars: Classification of Stars

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.

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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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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

Phase Retrieval Problem. Application to VLBI Mapping of Active Galactic Nuclei

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.

astro-ph.IM↗

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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arXiv2011

Searching for Possible Siblings of the Sun from a Common Cluster based on Stellar Space Velocities

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.

astro-ph.SR↗

arXiv2010

The investigation of absolute proper motions of the XPM Catalogue

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<B<22^m is something improved. The general procedure steps were followed as for XPM, but some of them are now performed on a more sophisticated level. The XPM-1.0 catalogue contains star positions, proper motions, 2MASS and USNO photometry of about 280 millions of the sources. We present some investigations of the absolute proper motions of XPM-1.0 catalogue and also the important information for the users of the catalogue. Unlike previous version, the XPM-1.0 contains the proper motions over the whole sky without gaps. In the fields, which cover the zone of avoidance or which contain less than of 25 galaxies a quasi absolute calibration was performed. The proper motion errors are varying from 3 to 10 mas/yr, depending on a specific field. The zero-point of the absolute proper motion frame (the absolute calibration) was specified with more than 1 million galaxies from 2MASS and USNO-A2.0. The mean formal error of absolute calibration is less than 1 mas/yr.

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arXiv2010

Determining the Orientation Parameters of the ICRS/UCAC2 System Using the Kharkov Catalog of Absolute Stellar Proper Motions

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: ω_{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.

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arXiv2009

Analysis of Peculiarities of the Stellar Velocity Field in the Solar Neighborhood

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.

astro-ph.CO↗

arXiv2009

Kinematics of Tycho-2 Red Giant Clump Stars

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) with an average distance of d=0.7 kpc, the contraction velocity is shown to be Kd= -3.5+-0.9 km/s; a noticeable vertex deviation, lxy = 9.1+-0.5 degrees, is also observed for them. For stars located well above 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.

astro-ph.GA↗

arXiv2009

Open Clusters ASCC21 as a Probable Birthplace of the Neutron Star Geminga

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 <= 10 pc at about t=-0.52 Myr. In addition, the trajectory of the neutron star Geminga passes at a distance about 25 pc from the center of the compact OB association lambda Ori at about t=-0.39 Myr, which is close to the age of the pulsar estimated from its timing.

astro-ph.GA↗

arXiv2008

Galactic Rotation Curve and the Effect of Density Waves from Data on Young Objects

Based on currently available data on the three-dimensional field of space velocities of young (<50 Myr) open star clusters and the radial velocities of HI clouds and star-forming (HII) regions, we have found the Galactic rotation curve in the range of Galactocentric distances 3 kpc <R<12 kpc using the first six terms of the Taylor expansion of the angular velocity of Galactic rotation in Bottlinger's equations. The Oort constants found are A= 15.5+-0.3 km/s/kpc and B=-12.2+-0.7 km/s/kpc. We have established that the centroid of the sample moves relative to the local standard of rest along the Galactic Y axis with a velocity of -6.2+-0.8 km/s. A Fourier spectral analysis of the velocity residuals from the derived rotation curve attributable to density waves reveals three dominant peaks with wavelengths of 2.5, 1.4, and 0.9 kpc and amplitudes of 4.7, 2.6, and 3.6 km/s, respectively. These have allowed us to estimate the distances between the density wave peaks, 1.9, 2.4, and 3.2 kpc as R increases, in agreement with the description of the density weave as a logarithmic spiral. The amplitude of the density wave perturbations is largest in the inner part of the Galaxy, about 9 km/s, and decreases to approximately 1 km/s in its outer part. A spectral analysis of the radial velocities of young open star clusters has confirmed the presence of periodic perturbations with an amplitude of 5.9+-1.1 km/s and a wavelength 1.7+-0.5 kpc. It shows that the phase of the Sun in the density wave is close to -90 degrees and the Sun is located in the interarm space near the outer edge of the Carina-Sagittarius arm.

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arXiv2007

Galactic Rotation Parameters from Data on Open Star Clusters

Currently available data on the field of velocities Vr, Vl, Vb for open star clusters are used to perform a kinematic analysis of various samples that differ by heliocentric distance, age, and membership in individual structures (the Orion, Carina--Sagittarius, and Perseus arms). Based on 375 clusters located within 5 kpc of the Sun with ages up to 1 Gyr, we have determined the Galactic rotation parameters Wo =-26.0+-0.3 km/s/kpc, W'o = 4.18+-0.17 km/s/kpc^2, W''o=-0.45+-0.06 km/s/kpc^3, the system contraction parameter K = -2.4+-0.1 km/s/kpc, and the parameters of the kinematic center Ro =7.4+-0.3 kpc and lo = 0+-1 degrees. The Galactocentric distance Ro in the model used has been found to depend significantly on the sample age. Thus, for example, it is 9.5+-0.7 kpc and 5.6+-0.3 kpc for the samples of young (<50 Myr) and old (>50 Myr) clusters, respectively. Our study of the kinematics of young open star clusters in various spiral arms has shown that the kinematic parameters are similar to the parameters obtained from the entire sample for the Carina-Sagittarius and Perseus arms and differ significantly from them for the Orion arm. The contraction effect is shown to be typical of star clusters with various ages. It is most pronounced for clusters with a mean age of 100 Myr, with the contraction velocity being Kr = -4.3+-1.0 km/s.

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