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1.
We report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope (GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ∼550 M⊙ with a linear size of 7 pc and an rms electron density of ∼110 cm−3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type O5.5. We also report detection of hydrogen recombination lines from the HII region at l = 24.83° and b = 0.1° at all observed frequencies near V lsr = 100 km s−1. We model the observed integrated line flux density as arising in the diffuse HII region and find that the best fitting model has an electron density comparable to that derived from the continuum. We also report detection of hydrogen recombination lines from two other HII regions in the field.  相似文献   

2.
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 = 8kpc, the peculiar velocity components for the Sun are (U ⊙, V ⊙, W ⊙) = (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 ω0″ = ?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 themodel of a two-armed spiral pattern, we have determined the pattern pitch angle $i = - 6_.^ \circ 5$ and the phase of the Sun in the spiral wave χ 0 = 150°.  相似文献   

3.
Bobylev  V. V.  Bajkova  A. T. 《Astronomy Letters》2019,45(6):331-340

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°.

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4.
We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found. The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic latitudes (|b|≥10°). At low galactic latitudes (|b|≤10°) most of unidentified X-ray sources (∼94%) lie at |b|≤2°. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties. These tables are intended as a useful tool for researchers interested in particular identifications.  相似文献   

5.
Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes, proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to the Galactic center R 0, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives. For R 0 = 8 kpc, we have found the circular velocity of the Sun to be V 0 = 243 ± 16 km s−1, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s−1 kpc−1 and B = −13.5 ± 1.4 km s−1 kpc−1. Our simulation of the influence of a spiral density wave has shown that the peculiar velocity of the Sun with respect to the local standard of rest and the component (V ⊙)LSR depend significantly on the Sun’s phase in the spiral wave.  相似文献   

6.
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   

7.
The rationale behind recent calibrations of the Cepheid PL relation using the Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent conclusions regarding a possible change in slope of the PL relation for short-period and long-period Cepheids are tied to a pathological distribution of HST calibrators within the instability strip. A recalibration of the period-luminosity relation is obtained using Galactic Cepheids in open clusters and groups, the resulting relationship, described by log L/L ⊙=2.415(±0.035)+1.148(±0.044)log P, exhibiting only the moderate scatter expected from color spread within the instability strip. The relationship is confirmed by Cepheids with HST parallaxes, although without the need for Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos parallaxes, albeit with concerns about the cited precisions of the latter. A Wesenheit formulation of W V =−2.259(±0.083)−4.185(±0.103)log P for Galactic Cepheids is tested successfully using Cepheids in the inner regions of the galaxy NGC 4258, confirming the independent geometrical distance established for the galaxy from OH masers. Differences between the extinction properties of interstellar and extragalactic dust may yet play an important role in the further calibration of the Cepheid PL relation and its application to the extragalactic distance scale.  相似文献   

8.
The three-dimensional Ogorodnikov-Milne model was used to investigate the local velocity field on the basis of the tangential velocities of more than 53 000 red giants which were identified as most probable Red Clump members from the Tycho-2 catalog. Galactic rotation parameters were determined for two star groups at the galactic latitudes |b| < 30° and |b| ≥ 30°. The galactic rotation of the first star group was found to have some peculiarities characterized by the statistically significant parameters of contraction (K = ?6.3 ± 1.1 km s?1 kpc?1) and phase shift (? = 6.9° ± 0.6°) in the Ogorodnikov-Miln model. The vertex deflection and the semiaxes of peculiar velocity ellipsoid were determined for both star groups together with the components of the Sun’s motion with respect to these groups. The greatest distinction between two groups manifests itself in the vertex deflection, which is equal to 5.9° ± 0.7° at |b| < 30° and 0.1° ± 0.6° at |b| ≥ 30°.  相似文献   

9.
We present the estimates of Galactic synchrotron and free-free emission power at intermediate and small scales (500 < l < 1000, 20′ < θ < 40′), based on the RATAN-600 radio telescope observations (SAO RAS). The observations were conducted in the frequency range of 2.3–11.2 GHz using the transit scan mode, in the declination range of 40.7° s δ < 42.3°. The power spectrum estimates of synchrotron and free-free components were obtained. They can be further used in the data processing stage of the high-resolution cosmological experiments like Planck.  相似文献   

10.
We have redetermined the kinematic parameters of the Gould Belt using currently available data on the motion of nearby young (log t < 7.91) open clusters, OB associations, and moving stellar groups. Our modeling shows that the residual velocities reach their maximum values of ?4 km s?1 for rotation (in the direction of Galactic rotation) and +4 km s?1 for expansion at a distance from the kinematic center of ≈300 pc. We have taken the following parameters of the Gould Belt center: R 0 = 150 pc and l 0 = 128°. The whole structure is shown to move relative to the local standard of rest at a velocity of 10.7 ± 0.7 km s?1 in the direction l = 274° ± 4° and b = ?1° ± 3°. Using the derived rotation velocity, we have estimated the virial mass of the Gould Belt to be 1.5 × 106 M ⊙.  相似文献   

11.
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   

12.
Bobylev  V. V.  Bajkova  A. T. 《Astronomy Letters》2019,45(9):580-592

We have studied the kinematic properties of the candidates for hot subdwarfs (HSDs) selected by Geier et al. from theGaiaDR2 catalogue. We have used a total of 12 515 stars with relative trigonometric parallax errors less than 30%. The HSDs are shown to have different kinematics, depending on their positions on the celestial sphere. For example, the sample of low-latitude (|b| < 20°) HSDs rotates around the Galactic center with a linear velocity V0 = 221 ± 5 km s?1. This suggests that they belong to the Galactic thin disk. At the same time, they lag behind the local standard of rest by ΔV☉ ~ 16 km s?1 due to the asymmetric drift. The high-latitude (|b| ≥ 20°) HSDs rotate with a considerably lower velocity, V☉ = 168 ± 6 km s?1. Their lagging behind the local standard of rest is already ΔV☉ ～ 40 km s?1. Based on the entire sample of 12 515 HSDs, we have found a positive rotation around the x axis significantly differing from zero with an angular velocity ω1 = 1.36±0.24 km s?1 kpc?1. We have studied the samples of HSDs that are complete within r < 1.5 kpc. Based on them, we have traced the evolution of the parameters of the residual velocity ellipsoid as a function of both latitude |b| and coordinate |z|. The following vertical disk scale heights have been found: h = 180 ± 6 and 290 ± 10 pc from the low- and high-latitude HSDs, respectively. A new estimate of the local stellar density Σout = 53 ± 4 M☉ kpc?2 has been obtained for zout = 0.56 kpc from the high-latitude HSDs.

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13.
We study the effect of systematic variations in stellar parallaxes over the celestial sphere on the results of a kinematic analysis of stellar proper motions. Our approach is based on the representation of stellar parallaxes by scalar spherical harmonics and on the decomposition of stellar proper motions into a system of vector spherical harmonics. We derive theoretical relations that relate the coefficients of the decomposition of stellar proper motions into toroidal and spheroidal harmonics to the coefficients of the decomposition of stellar parallaxes into scalar spherical harmonics. We have established that the systematic variations of parallaxes over the celestial sphere distort all parameters of the linear Ogorodnikov-Milne model and can be responsible for the appearance of beyond-the-model harmonics. We have performed a kinematic analysis of the proper motions of blue-white and red giants based on Hipparcos data. The parallaxes of blue-white giants show a strong dependence on Galactic latitude (with predominant contraction along the Galactic equator). In contrast, the deviations of the parallaxes from the mean for red giants are localized only in two regions of the celestial sphere. For these samples, the effect of parallax variations over the celestial sphere on kinematic parameters has turned out to be comparable to their rms errors. The global solutions performed using both samples have revealed strong beyond-the-model kinematic effects described by second-order toroidal harmonics and third-order spheroidal harmonics. Using the solutions performed separately in the northern and southern Galactic hemispheres, we have established that not the systematic variations of parallaxes over the celestial sphere but the retardation of Galactic rotation with increasing distance of stars from the principal Galactic plane is mainly responsible for the appearance of these harmonics. Based on these samples of stars, we have estimated the magnitude of the vertical Galactic rotation velocity gradient to be 18.0±2.9 and 22.7±2.2 km s?1 kpc?1, respectively.  相似文献   

14.
The kinematics and distribution of classical Cepheids within ∼3 kpc from the Sun suggest the existence of the outer ring R1R ′2 in the Galaxy. The optimum value of the solar position angle with respect to the major axis of the bar, θb, providing the best agreement between the distribution of Cepheids and model particles, is θb = 37° ±13°. The kinematical features obtained for Cepheids with negative galactocentric radial velocity VR are consistent with the solar location near the descending segment of the outer ring R2. The sharp rise of extinction toward of the Galactic center can be explained by the presence of the outer ring R1 near the Sun. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
Star counts and mean parallaxes as a function of B, V, R magnitudes down to 23 are presented. The data were computed by the use of two fundamental equations of stellar statistics. The assumed model considers the Galaxy as a symmetrical system with respect to its rotation axis and to its equatorial plane and as composed of the thin disk (main sequence and red giants), the thick disk and spheroid populations. Numbers of stars and mean parallaxes were derived in bins of galactic longitude and latitude of 30° and 10°, respectively. For the computation of the mean parallaxes depending on Galactic coordinates and magnitudes, series of products of Hermite and Legendre polynomials and of Fourier terms were used. The results of this paper may help in the planning of future survey missions and in the design of new telescopes. In addition, mean parallaxes can be used to derive corrections to absolute parallaxes and proper motions for any position in the sky.  相似文献   

16.
《Icarus》1986,67(2):251-263
511 Davida was observed with the technique of speckle interferometry at Steward Observatory's 2.3-m telescope on May 3, 1982. Assuming Davida to be a featureless triaxial ellipsoid, based on five 7-min observations its triaxial ellipsoid dimensions and standard deviations were found to be (465 ± 90) × (358 ± 58) × (258 ± 356) km. This shape is close to an equilibrium figure (a gravitationally shaped “rubble pile?”) suggesting a density of 1.4 ± 0.4 g/cm3. Simultaneously with the triaxial solution for the size and shape of Davida, we found its north rotational pole to lie within 29° of RA = 19h08m, Dec = +15° (λ = 291°, β = +37°). If Davida is assumed to be a prolate biaxial ellipsoid, then its dimensions were found to be (512 ± 100) × (334 ± 39) km, with a north pole within 16° of RA = 10h52m, Dec = +16° (λ = 322°, β = +32°). We derive and apply to Davida a new simultaneous amplitude-magnitude (SAM)-aspect method, finding, from photometric data only, axial ratios of a/b = 1.25 ± .02, b/c = 1.14 ± .03, and a rotational pole within 4° of λ = 307°, β = +32°. We also derive a (weighted) linearized form of the amplitude-aspect relation to obtain axial ratios and a pole. However, amplitudes must be known to better than .01 if the b/c or a/c ratios are desired to better than 10%. Combining the speckle and SAM results, we find for the Gehrels and Tedesco phase function a geometric albedo of .033 ± .009 and for the Lumme and Bowell function .041 ± .011, for a unified model of 437 × 350 × 307 km. Differences between the photometric and speckle axial ratios and poles are probably due to the effects of albedo structure over the asteroid; details on individual lightcurves support this conclusion.  相似文献   

17.
An anomalous velocity cloud nearl=349°,b=+3°, was investigated by Cugnon (1968). The authors made a new set of observations in order to obtain a more complete picture of the feature, including the region originally out of Cugnon's limit of observation. A comparison with optical and radio observations was made and several possibilities of interpretation as to the nature of the object were analyzed.  相似文献   

18.
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   

19.
We describe a method for determining the primordial helium abundance (Y p) from radio recombination lines and present results of the first stage of our measurements. We analyze the observational data for hydrogen and helium radio recombination lines from six Galactic H II regions obtained at different times. We have found Y p = 25.2−25.5% with an error of ±0.9% from four sources.  相似文献   

20.
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   

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