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1.
An analysis of the residual-velocity field of OB associations within 3 kpc of the Sun has revealed periodic variations in the radial residual velocities along the Galactic radius vector with a typical scale length of λ = 2.0 ± 0.2 kpc and a mean amplitude of f R = 7 ± 1 km s?1. The fact that the radial residual velocities of almost all OB associations in rich stellar-gas complexes are directed toward the Galactic center suggests that the solar neighborhood under consideration is within the corotation radius. The azimuthal-velocity field exhibits a distinct periodic pattern in the 0°<l<180° region, where the mean azimuthal-velocity amplitude is f θ = 6 ± 2 km s?1. There is no periodic pattern of the azimuthal-velocity field in the 180°<l<360° region. The locations of the Cygnus arm, as well as the Perseus arm, inferred from an analysis of the radial-and azimuthal-velocity fields coincide. The periodic patterns of the residual-velocity fields of Cepheids and OB associations share many common features. 相似文献
2.
We have studied a sample containing ~6000 OB stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The following parameters of the angular velocity of Galactic rotation have been found: Ω0 = 29.70 ± 0.11 km s-1 kpc-1, Ω'0 = -4.035 ± 0.031 km s-1 kpc-2, and Ω 0 = 0.620 ± 0.014 km s-1 kpc-3. The circular rotation velocity of the solar neighborhood around the Galactic center is V0 = 238 ± 5 km s-1 for the adopted Galactocentric distance of the Sun R0 = 8.0 ± 0.15 kpc. The amplitudes of the tangential and radial velocity perturbations produced by the spiral density wave are fθ = 4.4 ± 1.4 kms-1 and fR = 5.1 ± 1.2 kms-1, respectively; the perturbation wavelengths are λθ = 1.9 ± 0.5 kpc and λR = 2.1 ± 0.5 kpc for the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave is χ⊙ = -178° ± 12°.
相似文献3.
To study the peculiarities of the Galactic spiral density wave, we have analyzed the space velocities of Galactic Cepheids with propermotions 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 ⊙, v ⊙) = (7.6, 11.6) ± (0.8, 1.1) km s?1, the angular velocity of Galactic rotation Ω0 = 27.5 ± 0.5 km s?1 kpc?1 and its derivatives Ω′0 = ?4.12 ± 0.10 km s?1 kpc?2 and Ω″0 = 0.85 ± 0.07 km s?1 kpc?3, the amplitudes of the velocity perturbations in the spiral density wave f R = ?6.8 ± 0.7 and f θ = 3.3 ± 0.5 km s?1, the pitch angle of a two-armed spiral pattern (m = 2) i = ?4.6° ± 0.1° (which corresponds to a wavelength λ = 2.0 ± 0.1 kpc), and the phase of the Sun in the spiral density wave χ⊙ = ?193° ± 5°. The phase χ⊙ 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 ? Ω0| = 10 ± 1stat ± 3syst 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 ± 0.01. 相似文献
4.
The kinematics of the outer rings and pseudorings is determined by two processes: the resonance tuning and the gas outflow.
The resonance kinematics is clearly observed in the pure rings while the kinematics of the outflow is manifested itself in
the pseudorings. The direction of systematical motions in the pure rings depends on the position angle of a point with respect
to the bar major axis and on the class of the outer ring. The direction of the radial and azimuthal components of the residual
velocities of young stars in the Perseus, Carina, and Sagittarius regions can be explained by the presence of the outer pseudoring
of class R
1
R′2 in the Galaxy. We present models which reproduce the values and directions of the residual velocities of OB-associations
in the Perseus and Sagittarius regions and also model reproducing the directions of the residual velocities in the Perseus,
Sagittarius, and Carina regions. The kinematics of the Sagittarius region accurately defines the solar position angle with
respect to the bar elongation, θ
b = 45° ± 5°. 相似文献
5.
A sample of O- and B-type stars with Hipparcos astrometric data, ages computed from Strömgren photometry and radial velocities, has been used to characterize the structure, age and kinematics of the Gould Belt system. The local spiral structure of our galaxy is determined from this sample, and also from a sample of Hipparcos Cepheid stars. The Gould Belt, with an orientation with respect to the galactic plane ofi G = 16-22° and ΩG =275-295°, extends up to a distance of 600 pc from the Sun. Roughly the 60-65% of the O and B stars younger than 60 Myr in the solar neighbourhood belong to this structure. Our results indicate that the kinematical behaviour of this system is complex, with an expansion motion in the solar neighbourhood (R<300 pc).In the frame of the Lin's theory, and analysing the O and B stars further than 600 pc and the Cepheids, we found a galactic spiral structure characterized by a 4-arm spiral pattern with the Sun located atψ⊙ = 350-355 ± 30° – near the Sagittarius-Carina arm– and outside the corotation circle. The angular rotation speed of the spiral pattern was found to be Ωp = 31-32 ± 4 kms-1 kpc-1. 相似文献
6.
High angular-resolution measurements of directional fluxes of solar particles in space have been obtained with detectors aboard OGO-5 during the cosmic ray event of 18 November 1968. This is the only case on record for which sharply-defined directional observations of protons and electrons covering a wide rigidity range (0.3 MV to 1.5 GV) are available.The satellite experiment provided data for determining pitch-angle distributions with respect to the direction of the local interplanetary magnetic field lines during the lengthy highly anisotropic phase of the event. It was found that the unidirectional differential intensities j(θ) of 3- to 25-MeV protons varied in accordance with the relationship j(θ) = b0 + b1cosθ + b2cos2θ, where b0 and b1 ? 0, and b2, is positive, zero or negative. Soon after onset, 79–266-keV electrons arriving from the direction of the Sun displayed an anisotropic component with the intensity varying as cos θ. Later, a double-peaked distribution appeared at the lower energies, whereas the flux at the upper end of the range covered by the experiment became isotropic. These results have been interpreted in the light of the temporal flux profiles and the state of the interplanetary medium.The observation of the unusually large and long-lasting anisotropies lead to several conclusions including: (1) If injection of the solar particles was instantaneous, the diffusion coefficient was either constant or increasing with distance from the Sun. (2) If the solar source emitted particles over an extended period, and there is evidence to that effect, there was weak scattering in the region between the Sun and the Earth and a strong scattering region beyond the Earth's orbit. (3) Solar electrons were stored near the Sun. (4) The observed angular distribution of 200-MV protons in the magnetosheath was in good agreement with that deduced in an earlier analysis of polar orbiting satellite observations and trajectory calculations. 相似文献
7.
Based on kinematic data on masers with known trigonometric parallaxes and measurements of the velocities of HI clouds at tangential points in the inner Galaxy, we have refined the parameters of the Allen-Santillan model Galactic potential and constructed the Galactic rotation curve in a wide range of Galactocentric distances, from 0 to 20 kpc. The circular rotation velocity of the Sun for the adopted Galactocentric distance R 0 = 8 kpc is V 0 = 239 ± 16 km s?1. We have obtained the series of residual tangential, ΔV θ , and radial, V R , velocities for 73 masers. Based on these series, we have determined the parameters of the Galactic spiral density wave satisfying the linear Lin-Shu model using the method of periodogram analysis that we proposed previously. The tangential and radial perturbation amplitudes are f θ = 7.0±1.2 km s?1 and f R = 7.8±0.7 km s?1, respectively, the perturbation wave length is λ = 2.3±0.4 kpc, and the pitch angle of the spiral pattern in a two-armed model is i = ?5.2° ±0.7°. The phase of the Sun ζ ⊙ in the spiral density wave is ?50° ± 15° and ?160° ± 15° from the residual tangential and radial velocities, respectively. 相似文献
8.
A consistent study of the solar wind has been extended to a wide region of interplanetary space, up to distances from the Sun R ? 90 R s . Experiments are carried out with the radio telescopes of the Pushchino Radio Astronomy Observatory (Astrospace Center, Lebedev physical Institute, Russian Academy of Sciences): DKR-1000 (λ ≈ 2.7–2.9 m) and RT-22 (λ ≈ 1.35 cm), respectively. The radio-wave scattering characteristics, the scattering angle θ(R) and the scintillation index m(R), are studied. The formation of a steady supersonic solar wind is associated with a sequence of four stages whose scale in different solar wind streams changes within the range 10–23 R s , depending on the initial stream speed. These circumstances should be taken into account when predicting the state of the near space using data on the solar wind in regions of the interplanetary medium close to the Sun. 相似文献
9.
Karel A. van der Hucht 《Astrophysics and Space Science》2002,281(1-2):199-202
The recent VIIth Catalogue of Galactic Wolf-Rayet Stars lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries bring the census
to 234 WR stars. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in
the solar neighbourhood a projected surface density of 2.7 WR stars per kpc2, a N
WC/N
WN number ratio of 1.3, and a WR binary frequency of 40 %.The galactocentric distance (R
WR) distribution per subtype showsR
WN and R
WC decreasing with WN and WC subtypes.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
10.
This paper corrects and completes a previous study of the shape of the extinction curve in the visible and the value of RV. A continuous visible/infrared extinction law proportional to 1/λp with p close to 1 (± 0.4) is indistinguishable from a perfectly linear law (p = 1) in the visible within observational precision, but the shape of the curve in the infrared can be substantially modified. Values of p slightly larger than 1 would account for the increase of extinction (compared to the p = 1 law) reported for λ > 1 μ m and deeply affect the value of RV. In the absence of gray extinction RV must be 4.04 if p = 1. It becomes 3.14 for p = 1.25, 3.00 for p = 1.30, and 2.76 for p = 1.40. Values of p near 1.3 are also attributed to extinction by atmospheric aerosols, which indicates that both phenomena may be governed by similar particle size distributions. A power extinction law may harmonize visible and infrared data into a single, continuous, and universal interstellar extinction law (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
The combination of dispersion measures of pulsars, distances from the model of Cordes & Lazio (2002) and emission measures from the WHAM survey enabled a statistical study of electron densities and filling factors of the diffuse ionized gas (DIG) in the Milky Way. The emission measures were corrected for absorption and contributions from beyond the pulsar distance. For a sample of 157 pulsars at |b | > 5. and 60° < ℓ < 360°, located in mainly interarm regions within about 3 kpc from the Sun, we find that: (1) The average volume filling factor along the line of sight and the mean density in ionized clouds are inversely correlated: ( ) = (0.0184 ± 0.0011) –1.07 ± 0.03 for the ranges 0.03 < < 2 cm–3 and 0.8 > > 0.01. This relationship is very tight. The inverse correlation of and causes the well‐known constancy of the average electron density along the line of sight. As (z ) increases with distance from the Galactic plane |z |, the average size of the ionized clouds increases with |z |. (2) For |z| < 0.9 kpc the local density in clouds n c(z ) and local filling factor f (z ) are inversely correlated because the local electron density n e(z ) = f (z )n c(z ) is constant. We suggest that f (z ) reaches a maximum value of >0.3 near |z | = 0.9 kpc, whereas n c(z ) continues to decrease to higher |z |, thus causing the observed flattening in the distribution of dispersion measures perpendicular to the Galactic plane above this height. (3) For |z | < 0.9 kpc the local distributions n c(z ), f (z ) and (z ) have the same scale height which is in the range 250 < h ≲ 500 pc. (4) The average degree of ionization of the warm atomic gas (z ) increases towards higher |z | similarly to (z ). Towards |z | = 1 kpc, (z ) = 0.24 ± 0.05 and (z ) = 0.24 ± 0.02. Near |z | = 1 kpc most of the warm, atomic hydrogen is ionized. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
Results from kinematic solar dynamo models employing α ‐effect and turbulent pumping from local convection calculations are presented. We estimate the magnitude of these effects to be around 2–3 m s–1, having scaled the local quantities with the convective velocity at the bottom of the convection zone from a solar mixing‐length model. Rotation profile of the Sun as obtained from helioseismology is applied in the models; we also investigate the effects of the observed surface shear layer on the dynamo solutions. With these choices of the small‐ and large‐scale velocity fields, we obtain estimate of the ratio of the two induction effects, C α /C Ω ≈ 10–3, which we keep fixed in all models. We also include a one‐cell meridional circulation pattern having a magnitude of 10–20 m s–1 near the surface and 1–2 m s–1 at the bottom of the convection zone. The model essentially represents a distributed turbulent dynamo, as the α ‐effect is nonzero throughout the convection zone, although it concentrates near the bottom of the convection zone obtaining a maximum around 30° of latitude. Turbulent pumping of the mean fields is predominantly down‐ and equatorward. The anisotropies in the turbulent diffusivity are neglected apart from the fact that the diffusivity is significantly reduced in the overshoot region. We find that, when all these effects are included in the model, it is possible to correctly reproduce many features of the solar activity cycle, namely the correct equatorward migration at low latitudes and the polar branch at high latitudes, and the observed negative sign of B r B ϕ . Although the activity clearly shifts towards the equator in comparison to previous models due to the combined action of the α ‐effect peaking at midlatitudes, meridional circulation and latitudinal pumping, most of the activity still occurs at too high latitudes (between 5° … 60°). Other problems include the relatively narrow parameter space within which the preferred solution is dipolar (A0), and the somewhat too short cycle lengths of the solar‐type solutions. The role of the surface shear layer is found to be important only in the case where the α ‐effect has an appreciable magnitude near the surface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
Based on published sources, we have created a kinematic database on 220 massive (> 10 M ⊙) young Galactic star systems located within ≤3 kpc of the Sun. Out of them, ≈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%. 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 R 0 = 8kpc, V 0 = 259±16 km s?1, 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?1 and f θ = 7.9 ± 1.3 km s?1, respectively; the pitch angle for a two-armed spiral pattern i = ?6.0° ± 0.4°, with the wavelength of the spiral density wave near the Sun being λ = 2.6 ± 0.2 kpc; and the radial phase of the Sun in χ ⊙ = ?120° ± 4°. 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?1 and χ ⊙ = ?104° ± 6°. 相似文献
14.
F. Garzón P. L. Hammersley T. Mahoney X. Calbet M. J. Selby 《Astrophysics and Space Science》1994,217(1-2):177-180
The Two Micron Galactic Survey (TMGS) is the most sensitive large scale point source near infrared survey of the Galactic Plane yet attempted. The Galactic plane has been drift-scanned in several regions over the areas -5° <l < 30°, |b | 15° and 30° <l < 180°, |b | 5°. The survey is complete in the areas covered to magnitudem
k = +9.8. So far, a total area of 255 square degrees has been mapped and 500000 objects have been detected, the majority of these in the Galactic plane and with no visible counterparts. In this contribution we use data from the TMGS to probe the star distribution within the Galactic disk. 相似文献
15.
A. Brunthaler M.J. Reid K.M. Menten X.‐W. Zheng A. Bartkiewicz Y.K. Choi T. Dame K. Hachisuka K. Immer G. Moellenbrock L. Moscadelli K.L.J. Rygl A. Sanna M. Sato Y. Wu Y. Xu B. Zhang 《Astronomische Nachrichten》2011,332(5):461-466
Astrometric Very Long Baseline Interferometry (VLBI) observations of maser sources in the Milky Way are used to map the spiral structure of our galaxy and to determine fundamental parameters such as the rotation velocity (Θ0) and curve and the distance to the Galactic center (R0). Here, we present an update on our first results, implementing a recent change in the knowledge about the Solar motion. It seems unavoidable that the IAU recommended values for R0 and Θ0 need a substantial revision. In particular the combination of 8.5 kpc and 220 km s–1 can be ruled out with high confidence. Combining the maser data with the distance to the Galactic center from stellar orbits and the proper motion of Sgr A* gives best values of R0 = 8.3 ± 0.23 kpc and Θ0 = 239 or 246±7 km s–1, for Solar motions of V⊙ = 12.23 and 5.25 km s–1, respectively. Finally, we give an outlook to future observations in the Bar and Spiral Structure Legacy (BeSSeL) survey (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
G. A. Gontcharov 《Astronomy Letters》2010,36(8):584-595
The first results of the construction of a three-dimensional reddening map for stars within 1600 pc of the Sun are presented.
Analysis of the distribution of 70 million stars from the 2MASS catalog with the most accurate photometry on the (J-Ks)-Ks diagram supplemented with Monte Carlo simulations has shown that one of the maxima of this distribution corresponds to F-type
dwarfs and subgiants with a mean absolute magnitude M
Ks
= 2⊙
m
5. The shift of this maximum toward large J-Ks with increasing Ks reflects the reddening of these stars with increasing heliocentric distance. The distribution of the sample of stars over
Ks, l, and b cells with a statistically significant number of stars in each cell corresponds to their distribution over three-dimensional
spatial cells. As a result, the reddening E(J-Ks) has been determined with an accuracy of 0·
m
03 for spatial cells with a side of 100 pc. All of the known large absorbing clouds within 1600 pc of the Sun have manifested
themselves in the results obtained. The distances to the near and far edges of the clouds have been determined with a relative
accuracy of 15%. The cases where unknown clouds are hidden behind known ones on the same line of sight have been found. The
distance dependence of reddening is considered for various Galactic latitudes and longitudes. The absorbing matter of the
Gould Belt is shown to manifest itself at latitudes up to 40° and within 600 pc of the Sun. The size and influence of the
Gould Belt may have been underestimated thus far. The absorbing matter at latitudes up to 60° and within 1600 pc of the Sun
has been found to be distributed predominantly in the first and second quadrants in the southern hemisphere and in the third
and fourth quadrants in the northern hemisphere. The warping of the absorbing layer in the near Galaxy apparently manifests
itself in this way. A nonrandom orientation of the clouds relative to the Sun is possible. The mass of the baryonic dark matter
in solar neighborhoods can then be considerably larger than is generally believed. 相似文献
17.
Nelson L. Reginald Joseph M. Davila O. C. St. Cyr Douglas M. Rabin Madhulika Guhathakurta Donald M. Hassler Hadi Gashut 《Solar physics》2011,270(1):235-251
An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron
temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal
spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the
measured K-coronal spectra to interpret the observations. Results show electron temperatures of (1.10±0.05) MK, (0.70±0.08) MK,
and (0.98±0.12) MK, at 1.1 R
⊙ from Sun center in the solar north, east and west, respectively, and (0.93±0.12) MK, at 1.2 R
⊙ from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103±92) km s−1, (0+10) km s−1, (0+10) km s−1, and (0+10) km s−1. Since the observations were taken only at 1.1 R
⊙ and 1.2 R
⊙ from Sun center, these speeds, consistent with zero outflow, are in agreement with expectations and provide additional confirmation
that the spectral fitting method is working. The electron temperature at 1.1 R
⊙ from Sun center is larger at the north (polar region) than the east and west (equatorial region). 相似文献
18.
The spectral composition and spatial distribution of equatorial coronal emission near 304 Å is examined. Spectral scans indicate that the predominant line is from Si xi. Comparisons of observations with calculations of intensity changes with altitude indicate that collisional excitation is important near the Sun but that photoexcitation becomes dominant beyond about 1.3 R ⊙ from the solar center. Observed and calculated intensities are in approximate agreement for abundances and electron densities that are within the range of observed values. 相似文献
19.
Currently available data on the field of velocities V r , V l , V b 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 ω 0 = ?26.0 ± 0.3 km s?1 kpc?1, ω′0 = 4.18 ± 0.17 km s?1 kpc?2, ω″0 = ?0.45 ± 0.06 km s?1 kpc?3, the system contraction parameter K = ?2.4 ± 0.1 km s?1 kpc?1, and the parameters of the kinematic center R 0 = 7.4 ± 0.3 kpc and l 0 = 0° ± 1°. The Galactocentric distance R 0 in the model used has been found to depend significantly on the sample age. Thus, for example, it is 9.5 ± 0.7 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?1. 相似文献
20.
A study of the structure and kinematics of the Galaxy from Tautenburg Schmidt plates taken towards the Galactic centre (l = 17.0°, b = +0.8°) is presented. Proper motions and B, V magnitudes were determined for about 36 500 stars up to the limiting magnitude V = 16m.8 in a field of 8.95 square degrees. Proper motion accuracy of about 3 mas/year has been obtained for stars brighter than V = 15m. The rms errors of stellar magnitudes and (B–V) colours is about 0.1 mag. The majority of field stars in the survey are main sequence stars and red giants of the disk. They belong to the Local or Sagittarius-Carina arms, or they are located between these spiral arms. Comparing the modelled and observed distributions of magnitudes and colours, we specified the interstellar extinction determined in the preceding study of open clusters in this field. The luminosity function towards the Galactic centre was determined for stars with absolute magnitudes from -4m.35 to +9m. Kinematical and spatial distribution parameters up to 4 kpc from the Sun were obtained as a function of galactocentric distance. 相似文献