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The proper motions of stars in the main sequence and of luminosity class III giants are analyzed kinematically. A new method has been used for reliably separating all the parameters of the Ogorodnikov-Milne model based on representing the proper motions of the stars in coordinate systems whose poles lie on each of the three principal axes of the galactic trihedron. Solutions for stars in different spectral classes are obtained. The main sequence is found to subdivide into two zones (near and far stars) with a fairly sharp boundary at B-V=0.5. It is shown that the Parenago effect may be related to the different distances from the sun of the main sequence stars. 相似文献
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A method for determining the velocity field parameters free from the distortions due to the systematic variations of stellar parallaxes over the celestial sphere is proposed. The method is based on the approximation of parallaxes as a function of coordinates on the sphere using spherical harmonics and can be applied in those cases where the solar motion cannot be eliminated from the stellar proper motions. Numerical experiments have shown that our method is able to obtain accurate coordinates of the solar apex and to calculate the kinematic parameters of the Ogorodnikov-Milne model to within three coefficients of the decomposition of parallaxes into first-order spherical harmonics. Examples of applying the method to the stellar proper motions of the Hipparcos catalogue, which admits checking the results using trigonometric parallaxes, are provided. Such a check has been found to yield a positive result only for nearby stars at heliocentric distances that do not exceed 400 pc and for which the parallaxes were determined with a relative error of at least 30%. An interesting feature of this method is the possibility to construct the shape of the figure which is formed by the deviations of the parallaxes from the sphere corresponding to the average parallaxes of the stars under consideration. It should be specially emphasized that all of this is done in the complete absence of information about the stellar parallaxes. The “solar terms” of the stellar proper motions that are formed by the products of the parallaxes by the solar motion components relative to the centroid of stars are the main source of information about the parallaxes here. 相似文献
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We apply vector spherical functions to problems of stellar kinematics. Using these functions allows all of the systematic components in the stellar velocity field to be revealed without being attached to a specific physical model. Comparison of the theoretical decomposition coefficients of the equations for a particular kinematical model with observational data can provide precise information about whether the model is compatible with the observations and can reveal systematic components that are not described by this model. The formalism of vector spherical functions is particularly well suited for analyzing the present and future (e.g., GAIA) catalogs containing all three velocity vector components: the propermotions in both coordinates and the radial velocity. We show that there are systematic components in the proper motions of Hipparcos stars that cannot be interpreted in terms of the linear Ogorodnikov-Milne model. The same result is also confirmed by an analysis of the radial velocities for these stars. 相似文献
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We use vector spherical harmonics for a kinematic analysis of the proper motions of stars from the Hipparcos, Tycho-2, and UCAC3 catalogues in the northern and southern Galactic hemispheres. We have found that the statistically reliable values of the Ogorodnikov-Milne model parameters M 32 + and M 32 ? have different signs in different hemispheres. This is a consequence of the Galaxy??s rotational retardation with distance from the principal Galactic plane. Based on various samples of stars from the above catalogues, we have obtained the following estimate for the magnitude of the vertical gradient of Galactic rotation velocity in the solar neighborhoods: (20.1 ± 2.9) < |?V??/?z| < (49.2 ± 0.8) km s?1 kpc?1. Another result that is revealed by our analysis of the parameters M 13 ? and M 13 + in different Galactic hemispheres is that the vertical gradient of expansion velocity for the stellar system ?V R /? z is positive in the northern hemisphere and negative in the southern one. This suggests that the expansion velocity V R increases with distance fromthe Galactic plane. We show that both these gradients give rise to an apparent acceleration of the solar motion along the x and y axes of the rectangular Galactic coordinate system. Our analysis of the parameters M 21 ? and M 12 + shows no significant differences in both hemispheres and has allowed us to determine the Oort parameters, to estimate the Galactic rotation velocity and period in the solar neighborhood, and to calculate the ratio of the epicyclic frequency to the angular velocity of Galactic rotation in the solar neighborhood. The derived diagonal elements of the velocity field deformation tensor suggest that the orientation of the rectangular Galactic coordinate system in space must be determined by taking into account not only the geometrical factors but also the dynamical ones. All these results agree well with these quantities estimated over the entire sphere by various authors. 相似文献
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As a check on the differentiation processes of planetesimals the experiment Tsarev was carried out. The main problems of the experiment were: investigation of melting and liquation processes in the melt of primitive meteorite substance; analysis of the composition of metallic and silicate phases, including the distribution of rare-earth elements and comparison of the obtained phase with iron and differentiated meteorite composition. The heating of a sample of the L-chondrite Tsarev (volume 15 cm3) was produced by intensive microwave radiation because this method of heating provides the possibility of uncontact entry of energy into a sufficiently large sample. Upon the heating of the meteorite Tsarev (with the maximum temperature 1500±50K) this sample was melted and two phases appeared and were separated in the gravity field: the composition of Fe-Ni-S phase includes 15 rare-earth elements and the silicate phase is composed of the main oxides. There is also clear evidence for the presence of liquation processes of second order, e.g. separation of Fe-Ni from Fe-S component. 相似文献
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V. V. Vityazev 《Astrophysics and Space Science》1991,177(1-2):213-214
The proper motions of 512 stars reduced to the system of FK5 were used for the determination of the velocity components X,Y,Z of the solar motion, Dort's constants A,B, and corrections n, k to Newcomb's precession values. It was found that the transition from FK4 to FK5 gives negligible and unsignificant changes to all the determined quantities. 相似文献
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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
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Astronomy Letters - The systematic differences between the stellar positions and proper motions of the XPM and UCAC4 catalogs have been obtained in the form of decompositions into vector spherical... 相似文献