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1.
G. A. Gontcharov 《Astronomy Letters》2011,37(10):707-717
Based on multicolor photometry from the 2MASS and Tycho-2 catalogues, we have produced a sample of 38 368 branch red giants
that has less than 1% of admixtures and is complete within 500 pc of the Sun. The sample includes 30 671 K giants, 7544Mgiants,
49 C giants, and 104 suspected supergiants or S stars. The photometric distances have been calculated for K, M, and C stars
with an accuracy of 40%. Tycho-2 proper motions and PCRV radial velocities are used to analyze the stellar kinematics. The
decrease in the stellar distribution density with distance from the Galactic equator approximated by the barometric law, contrary
to the Besanconmodel of the Galaxy, and the kinematic parameters calculated using the Ogorodnikov-Milne model characterize
the overwhelming majority of the selected K and M giants as disk stars with ages of more than 3 Gyr. A small number of K and
M giants are extremely young or, conversely, thick-disk ones. The latter show a nonuniform distribution in the phase space
of coordinates and velocities, arguing against isothermality and full relaxation of the disk and for the theory of dynamical
streams or superclusters. The spatial distribution and kinematics of the selected C stars force us to consider them as asymptotic
branch giants with masses of more than 2M
⊙ and ages of less than 2 Gyr probably associated with the Gould Belt. The offset of the Sun above the Galactic equator has
been found from the distribution of stars to be 13 ± 2 pc, which coincides with the previously obtained value for the clump
red giants. 相似文献
2.
V. V. Bobylev A. S. Stepanishchev A. T. Bajkova G. A. Gontcharov 《Astronomy Letters》2009,35(12):836-849
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?1 kpc?1 and B = ?12.0±0.2 km s?1 kpc?1. 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?1; a noticeable vertex deviation, l xy = 9 · o 1 ± 0 · o 5, 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?1 and l xy = 4 · o 9 ± 0 · o 6. 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?1 kpc?1, which we associate with the warp of the Galactic stellar-gaseous disk. 相似文献
3.
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°–25° with respect to the Galactic center-Sun direction and a semimajor axis of no more than 3 kpc. 相似文献
4.
G. A. Gontcharov 《Astronomy Letters》2008,34(1):7-16
The Tycho-2 proper motions and five-band Tycho-2 and 2MASS photometry for approximately 2.5 million common stars have been
used to select OB stars and to determine the extinction and photometric distance for each of them. We have selected 37 485
stars and calculated their reddenings based on their positions in the two-color V
T
-H, J-Ks diagrams relative to the zero-age main sequence and the theoretical reddening line for B5 stars. Tests confirm that the selected
stars belong to the spectral types O-B with a small admixture of later types. We calculate the extinction coefficient R and its variations with Galactic longitude based on the positions of the selected stars in the two-color B
T
-V
T
, V
T
-Ks diagram. The interstellar extinction for each star is calculated as the product of the reddening found and the coefficient
R. The extinction and its variations with Galactic longitude agree well with the extinction based on the model by Arenou et
al. (1992). Calibration of the relation between the absolute magnitude and reduced proper motion V
T
− + 5 + 5 log μ for Hipparcos stars has allowed us to calculate the absolute magnitudes and photometric distances for the selected stars.
The distances found agree with those derived from the Hipparcos parallaxes within 500 pc. The distribution of the stars and
the extinction variations with distance found show that the selected stars form an almost complete sample of stars with spectral
types earlier than B5 within about 750 pc of the Sun. The sample includes many noticeably reddened stars in the first and
second Galactic quadrants that are absent from the Hipparcos and Tycho Spectral Types Catalogues. This slightly changes the
pattern of the distribution of OB stars compared to the classical pattern based on Hipparcos.
Original Russian Text ? G.A. Goncharov, 2008, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2008, Vol. 34, No. 1, pp. 10–20. 相似文献
5.
Based on the Ogorodnikov-Milne model, we analyze the proper motions of Tycho-2 and UCAC2 stars. We have established that the model component that describes the rotation of all stars under consideration around the Galactic y axis differs significantly from zero at various magnitudes. We interpret this rotation found using the most distant stars as a residual rotation of the ICRS/Tycho-2 system relative to the inertial reference frame. For the most distant (d≈900 pc) Tycho-2 and UCAC2 stars, the mean rotation around the Galactic y axis has been found to be M 13 ? =?0.37±0.04 mas yr?1. The proper motions of UCAC2 stars with magnitudes in the range 12–15m are shown to be distorted appreciably by the magnitude equation in μα cos δ, which has the strongest effect for northern-sky stars with a coefficient of ?0.60±0.05 mas yr?1 mag?1. We have detected no significant effect of the magnitude equation in the proper motions of UCAC2 stars brighter than ≈11m. 相似文献
6.
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: 2 kpc. 相似文献
7.
G. A. Gontcharov 《Astronomy Letters》2012,38(1):12-24
Multicolor photometry from the Tycho-2 and 2MASS catalogues for 11 990 OB and 30 671 K-type red giant branch stars is used
to detect systematic large-scale variations of the interstellar extinction law within the nearest kiloparsec. The characteristic
of the extinction law, the total-to-selective extinction ratio Rv, which also characterizes the size and other properties of interstellar dust grains, has been calculated for various regions
of space by the extinction law extrapolation method. The results for the two classes of stars agree: the standard deviation
of the “red giants minus OB” Rv differences within 500 pc of the Sun is 0.2. The detected Rv variations between 2.2 and 4.4 not only manifest themselves in individual clouds but also span the entire space near the
Sun, following Galactic structures. In the Local Bubble within about 100 pc of the Sun, Rv has a minimum. In the inner part of the Gould Belt and at high Galactic latitudes, at a distance of about 150 pc from the
Sun, Rv reaches a maximum and then decreases to its minimum in the outer part of the Belt and other directions at a distance of
about 500 pc from the Sun, returning to its mean values far from the Sun. The detected maximum of Rv at high Galactic latitudes is important when allowance is made for the interstellar extinction toward extragalactic objects.
In addition, a monotonic increase in Rv by 0.3 per kpc toward the Galactic center has been found near the Galactic equator. It is consistent with the result obtained
by Zasowski et al. (2009) for much of the Galaxy. Ignoring the Rv variations and traditionally using a single value for the entire space must lead to systematic errors in the calculated
distances reaching 10%. 相似文献
8.
G. A. Gontcharov 《Astronomy Letters》2009,35(9):638-650
The stellar composition of the Tycho-2 Catalogue in the range B-V = 0·
m
75–1·
m
25 has been reproduced through Monte Carlo simulations. For young and old stars of the red giant clump (RGC), the red giant
branch, subgiants, red dwarfs, and thick-disk giants, we have specified the distributions in coordinates, velocities, B-V, and M
V
as a function of B-V and calculated their reduced proper motions, photometric distances from the (B-V)-M
V
calibration, and photoastrometric distances from the reduced proper motion-M
V
calibration. Our simulations have shown the following: (1) a sample of thin-disk giants within 500 pc with an admixture of
less than 10% of other stars can be produced; (2) a sample of dwarfs within 100 pc almost without any admixture of other stars
can be produced; (3) the Local Spiral Arm affects the RGC composition of any magnitude-limited catalog in favor of giants
younger than 2 Gyr; (4) the samples produced using reduced proper motions can be used for kinematic studies, provided that
the biases of the quantities being determined are simulated and taken into account; (5) the photometric distances correlate
with the photoastrometric ones because of the correlation between the proper motion and magnitude; (6) the photometric distances
are closer to the true ones for the red giant branch and red dwarfs as the categories of stars with a clear (B-V)-M
V
relation, while the photoastrometric distances are closer to the true ones for the RGC, subgiants, and thick-disk giants;
(7) the calculated distances differ systematically from the true ones, but they can be used to analyze the three-dimensional
distribution of stars. Our simulations confirm the validity of our previous selection of RGC stars from Tycho-2. 相似文献
9.
A method for a kinematic analysis of stellar radial velocities using spherical harmonics is proposed. This approach does not depend on the specific kinematic model and allows both low-frequency and high-frequency kinematic radial velocity components to be analyzed. The possible systematic variations of distances with coordinates on the celestial sphere that, in turn, are modeled by a linear combination of spherical harmonics are taken into account. Theoretical relations showing how the coefficients of the decomposition of distances affect the coefficients of the decomposition of the radial velocities themselves have been derived. It is shown that the larger the mean distance to the sample of stars being analyzed, the greater the shift in the solar apex coordinates, while the shifts in the Oort parameter A are determined mainly by the ratio of the second zonal harmonic coefficient to the mean distance to the stars, i.e., by the degree of flattening of the spatial distribution of stars toward the Galactic plane. The distances to the stars for which radial velocity estimates are available in the CRVAD-2 catalog have been decomposed into spherical harmonics, and the existing variations of distances with coordinates are shown to exert no noticeable influence on both the solar motion components and the estimates of the Oort parameter A, because the stars from this catalog are comparatively close to the Sun (no farther than 500 pc). In addition, a kinematic component that has no explanation in terms of the three-dimensional Ogorodnikov-Milne model is shown to be detected in the stellar radial velocities, as in the case of stellar proper motions. 相似文献
10.
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 ≈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. 相似文献
11.
《New Astronomy》2019
We exploit information, including velocities from the fifth data release of the RAdial Velocity Experiment (RAVE), to find evidence of the Lin–Shu type tightly wound spiral density waves in the nearby Galactic disk. The Kunder et al. (2017) catalogue of 471117 stars with derived spectrophotometric distances and line-of-sight velocities are explored to find the geometry and parameters of the velocity field in the extended solar neighborhood. Possible existence of noncircular systematic motions of selected 37,354 disk objects within 2 kpc from the Sun and 500 pc from the Galactic mid-plane together with the ordinary differential rotation are assumed. Both the pitch angle of spiral arms and the spatial location of the Sun within the density–wave pattern and the deviations of the motion of objects from the circular motion are calculated by fitting the stellar line-of-sight velocities in RAVE DR5 with the simplest linear perturbation density–wave model. Two radial wavelengths of the wave pattern of about 0.5 kpc and 1.5 kpc in the solar vicinity are found. We argue that the spiral structure of the Galaxy has an oscillating nature corresponding to a concept of the fairly unstable, low amplitude, tightly wound, and rigidly rotating density waves. 相似文献
12.
G. A. Gontcharov 《Astronomy Letters》2016,42(7):445-459
Photometry from the Tycho-2, 2MASS, andWISE catalogues for clump and branch giants at a distance up to 25 kpc toward the Galactic poles has allowed the variations of various characteristics of the infrared interstellar extinction law with distance to be analyzed. The results obtained by the extinction law extrapolation method are consistent for different classes of stars and different characteristics as well as with previous studies. The conventional extinction law with a low infrared extinction is characteristic of only a thin layer no farther than 100 pc from the Galactic plane and of two thin layers near Z = ?600 and +500 pc. Far from the Galactic plane, in the Galactic halo, the infrared extinction law is different: the extinction in the Ks, W1, W2, W3, and W4 bands is, respectively, 0.17, 0.16, 0.16, 0.07, and 0.03 of the extinction in the V band. The accuracy of these coefficients is 0.03. If the extinction law reflects primarily the grain size distribution, then the fraction of large dust grains far from the Galactic plane is greater than that in the circumsolar interstellar medium. 相似文献
13.
Accurate two-colour photometry and proper motions of 7096 young X-ray stars in the ROSAT All-Sky Survey Bright Star Catalogue, version 1RXS, are extracted from the Tycho-2 Catalogue. The sample is dominated by red main-sequence and possibly pre-main-sequence stars. On a global proper motion convergence map, two features are very prominent: the nearby section of the Gould Belt and the Hyades convergent point. The appearance of the Gould Belt feature with its peak at ( l =2443, b =−126) is quite similar to that of Hipparcos OB stars. When only stars with proper motions drawing close to that point are selected, strong concentrations of stars in the direction of the Sco–Cen complex are found. Another concentration, not corresponding to any known OB association, is detected between the position of the Lower Centaurus Crux and Vela OB2 associations. It is a new young moving group located in Carina and Vela, and a near extension of the Sco–Cen complex. Contrary to the classical Gould Belt OB associations, the Carina–Vela moving group has a considerable geometric depth, the closest members being as near as 30 pc from the Sun. IC 2391, one of the youngest and closest open clusters on the sky, is a part of the Carina–Vela moving group. The Carina–Vela moving group does not link the Sco–Cen complex with the Vela OB associations, because the latter is much more distant than the outer limit of the sample. It is more likely that the young late-type population of the Scorpio–Centaurus–Carina moving group stretches towards the Sun and possibly beyond it. 相似文献
14.
The motions of the components of wide binary stars in the solar neighborhood in the regular Galactic gravitational field on time scales ～1010 yr have been studied numerically. The regions of restricted motions of the components in wide pairs have been found depending on the initial conditions: the magnitude of the relative velocity of the components, their mutual distance, and the inclination of the relative velocity vector to the Galactic plane. The size of the main part of the region of restricted motions is approximately equal to the tidal radius. Profound changes in the eccentricity of the binary orbit occur at inclinations close to 90°, which can lead to close approaches of the stars with a pericenter distance less than 1 AU. In the case of retrograde motions (the binary rotates in a direction opposite to the Galactic rotation), there is a region of restricted motions extending at least to 10 pc. Examples of the trajectories of relative motion of the stars and the change in osculating orbital elements are given for systems with restricted motions. 相似文献
15.
An attempt is made to determine the scale height of the thin Galactic disk in the solar neighborhood using various stellar samples from the accurate astrometric data of the Hipparcos satellite. Using the Tycho color indices and considering the completeness of the samples, several samples were selected from the main sequence and the horizontal branch. Based on two rather complete samples, it is found that the scale height of the Galactic disk defined by the O-B type main sequence stars is 103.1 ± 3.0 pc and the Sun is located at height of 15.2 ± 7.3 pc above its mean plane; while the scale height of the Galactic disk defined by the horizontal branch stars is 144.0 the ±10.0 pc and the Sun is located at height 3.5 ± 5.4 pc above the mean plane. Owing to the incompleteness of observational samples, it is not possible to use the main sequence stars of spectral types A, F, G, K and M to make a reliable determination of the scale height. 相似文献
16.
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 Ω'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)⊙ = (9.28, 20.35, 7.36) ± (0.05, 0.07, 0.05) km s?1, the angular velocity of Galactic rotation Ω0 = 27.24 ± 0.30 km s?1 kpc?1, and its first derivative Ω'0 = ?3.77 ± 0.06 km s?1 kpc?2; here, the circular rotation velocity of the Sun around the Galactic center is V0 = 218 ± 6 km s?1 kpc (for the adopted distance R0 = 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 Ω'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. 相似文献
17.
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?1. 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. 相似文献
18.
In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the absolute proper motions of more than 11000 stars with respect to 3000 galaxies and their stellar magnitudes in the B, V Johnson system are determined in two sky regions near the North Galactic Pole (NGP) by means of Tautenburg Schmidt plates. The limiting and completing apparent stellar magnitudes are B = 20.4 and 18.3 mag, the overall and the investigated sky areas are 16.4 and 14.6 square degrees, respectively. Distances have been determined using the stellar magnitudes, colours, proper motions and reduced proper motions. Stellar kinematics, eccentricities of Galactic orbits, spatial distribution and changes of these characteristics with Z-distance from the Galactic plane are obtained up to 15 kpc. Four subsystems distinguished in the NGP direction, respectively with semithicknesses of 0.25, 0.38, 0.67, 1.48 kpc and density ellipsoid axial ratios of 0.09, 0.20, 0.28, 0.49 show mean velocities in the Galactic rotation direction relative to the LSR of 5.6 ± 0.6, − 11.0 ± 0.6, − 62.5 ± 1.2, − 181.6 ± 4.4 km/s, and ages of 0.1, 0.4, 0.9, 1 of the Galaxy age. 相似文献
19.
In this paper we combine information on photometry, radial velocities and proper motions to study the nature of the suspected open cluster Cr 135. For the first time we introduce proper motions of a large number of stars in the region of Cr 135 into the discussion. The proper motions taken from the PPM catalogue favour the hypothesis that Cr 135 is a real open cluster with at least 12 members at a distance of 300 pc having a space motion U, V, W of (−11, −13, −15) km s−1. But still more accurate observations are needed to separate it from the field stars without any doubt. 相似文献
20.
We solve the problem on a kinematic analysis of the three-dimensional velocity field of stars from zonal catalogues, i.e.,
catalogues in which the stars are presented at all right ascensions in some declination zones. We have constructed a system
of vector spherical harmonics with the properties of completeness and orthogonality for a chosen declination zone. We suggest
a method that allows the Ogorodnikov-Milne model parameters in the Galactic coordinate system to be estimated by analyzing
the proper motions and radial velocities of stars in the equatorial coordinate system. The vector spherical harmonics are
shown to have the following advantages over the standard approach based on a direct leastsquares estimation of the parameters
for a specific model. First, in contrast to the standard approach, the new method can reveal all systematic components of
the velocity field irrespective of a particular model. Second, it allows one to get rid of the correlation between the sought-for
parameters, which presents a serious problem for the conventional method in the case of zonal catalogues. Third, the method
of vector spherical harmonics allows the kinematic parameters to be estimated at least by two techniques. Comparison of these
two solutions makes it possible to test the standard kinematic model for compatibility with the observational data. The developed
method has been tested on the basis of numerical experiments and applied for a kinematic analysis of the proper motions of
Tycho-2 stars in the southern hemisphere for which the parallaxes can be estimated using data from the Tycho-2 Spectral Type
Catalogue. 相似文献