The galactic constants and rotation curve from molecular-gas observations

We obtained the photometric distances and radial velocities for the molecular gas for 270 star-forming regions and estimated the distance to the Galactic center from ten tangent points to be R₀ = 8.01 ± 0.44 kpc. Estimates of R₀ derived over the last decade are summarized and discussed; the average value is R₀ = 7.80 ± 0.33 kpc. We analyze deviations from axial symmetry of the gas motion around the Galactic center in the solar neighborhood. Assuming a flat rotation curve, we obtain Θ₀ ～ 200 km/s for the circular velocity of the Sun from regions beyond the Perseus arm. We used these Galactic constants to construct the Galactic rotation curve. This rotation curve is flat along virtually its total extent from the central bar to the periphery. The velocity jump in the corotation region of the central bar in the first quadrant is 20 km/s. We present analytical formulas for the rotation curves of the Northern and Southern hemispheres of the Galaxy for R₀ = 8.0 kpc and Θ₀ = 200 km/s.     

The OSACA database and a kinematic analysis of stars in the solar neighborhood

We transformed radial velocities compiled from more than 1400 published sources, including the Geneva-Copenhagen survey of the solar neighborhood (CORAVEL-CfA), into a uniform system based on the radial velocities of 854 standard stars in our list. This enabled us to calculate the average weighted radial velocities for more than 25000 HIPPARCOS stars located in the local Galactic spiral arm (Orion arm) with a median error of ±1 km/s. We use these radial velocities together with the stars’ coordinates, parallaxes, and proper motions to determine their Galactic coordinates and space velocities. These quantities, along with other parameters of the stars, are available from the continuously updated Orion Spiral Arm Catalogue (OSACA) and the associated database. We perform a kinematic analysis of the stars by applying an Ogorodnikov-Milne model to the OSACA data. The kinematics of the nearest single and multiple main-sequence stars differ substantially. We used distant (-r ≈ 0.2 kpc) stars of mixed spectral composition to estimate the angular velocity of the Galactic rotation, ω_o = ?25.7 ± 1.2 kms^?1 kpc^?1, and the vertex deviation, l = 13° ± 2°, and detected a negative K effect. This negative K effect is most conspicuous in the motion of A0–A5 giants and is equal to K = ?13.1 ± 2.0 kms^?1 kpc^?1.     

Galactic parameters derived from open-cluster data

The components U₀ and V₀ of the solar motion and the Oort constant A₀ are determined using the data of a homogeneous open-cluster catalog with corrected distance moduli. The results are based on a sample of 146 open clusters with known radial velocities located in the Galactic plane (b<7°) within 4 kpc of the Sun. The solar Galactocentric distance R₀ is determined using two kinematic methods. The following results are obtained: A₀=17.0±0.9 km/s kpc, U₀=10.5±1.0 km/s, V₀=11.5±1.1 km/s, R₀=8.3±0.3 pc.     

On the spiral structure of the Milky Way Galaxy

We consider a possible scheme of the overall spiral structure of the Galaxy using data on the distribution of neutral (atomic), molecular, and ionized hydrogen. Our analysis assumes that the spiral structure is symmetric, i.e., that the spiral arms are translated into each other via a rotation about the Galactic center by 180° (a two-arm pattern) or 90° (a four-arm pattern). In the inner region, the observations are best represented with a four-arm spiral pattern, associated with all-Galaxy spiral density waves. The initial position is that of the Carina arm, reliably determined from distances to HII regions and from HI and H₂ radial velocities. This pattern continues in quadrants III and IV with weak outer HI arms; from their morphology, the Galaxy should be considered an asymmetric multi-arm spiral. The knee-like shape of the outer arms, which consist of straight segments, may indicate that these arms are transient formations that appeared due to gravitational instability in the gaseous disk. The distances between HI superclouds in the two arms that are brightest in neutral hydrogen, the Carina and Cygnus (Outer) arms, are concentrated near two values, suggesting the presence of a regular magnetic field in these arms.     

Globular cluster subsystems in the galaxy

Data from the literature are used to construct a homogeneous catalog of fundamental astrophysical parameters for 145 globular clusters of the Milky Way Galaxy. The catalog is used to analyze the relationships between chemical composition, horizontal-branch morphology, spatial location, orbital elements, age, and other physical parameters of the clusters. The overall globular-cluster population is divided by a gap in the metallicity function at [Fe/H]=?1.0 into two discrete groups with well-defined maxima at [Fe/H]=?1.60±0.03 and ?0.60±0.04. The mean spatial-kinematic parameters and their dispersions change abruptly when the metallicity crosses this boundary. Metal-poor clusters occupy a more or less spherical region and are concentrated toward the Galactic center. Metal-rich clusters (the thick disk subsystem), which are far fewer in number, are concentrated toward both the Galactic center and the Galactic plane. This subsystem rotates with an average velocity of V _rot=165±28 km/s and has a very steep negative vertical metallicity gradient and a negligible radial gradient. It is, on average, the youngest group, and consists exclusively of clusters with extremely red horizontal branches. The population of spherical-subsystem clusters is also inhomogeneous and, in turn, breaks up into at least two groups according to horizontal-branch morphology. Clusters with extremely blue horizontal branches occupy a spherical volume of radius ～9 kpc, have high rotational velocities (V _rot=77±33 km/s), have substantial and equal negative radial and vertical metallicity gradients, and are, on average, the oldest group (the old-halo subsystem). The vast majority of clusters with intermediate-type horizontal branches occupy a more or less spherical volume ≈18 kpc in radius, which is slightly flattened perpendicular to the Z direction and makes an angle of ≈30° to the X-axis. On average, this population is somewhat younger than the old-halo clusters (the young-halo subsystem), and exhibits approximately the same metallicity gradients as the old halo. As a result, since their Galactocentric distance and distance from the Galactic plane are the same, the young-halo clusters have metallicities that are, on average, Δ[Fe/H] ≈0.3 higher than those for old-halo clusters. The young-halo subsystem, which apparently consists of objects captured by the Galaxy at various times, contains many clusters with retrograde orbits, so that its rotational velocity is low and has large errors, V _rot=?23±54 km/s. Typical parameters are derived for all the subsystems, and the mean characteristics of their member globular clusters are determined. The thick disk has a different nature than both the old and young halos. A scenario for Galactic evolution is proposed based on the assumption that only the thick-disk and old-halo subsystems are genetically associated with the Galaxy. The age distributions of these two subsystems do not overlap. It is argued that heavy-element enrichment and the collapse of the proto-Galactic medium occurred mainly in the period between the formation of the old-halo and thick-disk subsystems.     

The generation of low-energy cosmic rays in molecular clouds

Arguments are presented in support of the idea that the total energy losses of cosmic rays passing through molecular clouds can exceed the energy production due to the action of shocks in supernovae. Galactic cosmic rays interacting with the surface layers of molecular clouds can be efficiently reflected, so that they do not penetrate into the depths of the clouds. Low-energy cosmic rays (E < 1 GeV) that can produce the primary ionization of the molecular-cloud gas can be generated inside such clouds by numerous shocks arising due to supersonic turbulence.     

Observational manifestations of gaseous baryon dark matter

The paper considers possible observational implications of the presence of dark matter in the Galaxy in the form of dense gas clouds—clumpuscules with masses M _c ～10^?3 M _⊙ and radii R _c～3×10¹³ cm. The existence of such clouds is implied by modern interpretations of extreme scattering events—variations in quasar radio fluxes due to refraction in dense plasma condensations in the Galactic halo. The rate of collisions between these clouds is shown to be rather high: from 1 to 10M _⊙ per year is ejected into the interstellar medium as a result of such collisions. The optical continuum and 21-cm emission from hot post-collision gas could be observable. Gas clouds composed of dark matter could be formed around O stars in an H II region with radius R～30 pc and emission measure EM?20 cm^?6 pc. They could also be observable in the H_α line. The evaporation of clumpuscules by external ionizing radiation could be a substantial source of matter for the interstellar medium. Assuming that the total mass of matter entering the interstellar medium over the Hubble time does not exceed the mass of luminous matter in the Galaxy, upper limits are found for the cloud radii (R _c<3.5×10¹² cm) and the contribution of clouds to the surface density of the Galaxy (<50M _⊙pc^?2). Dissipation of the kinetic energy of matter lost by clumpuscules could provide an efficient mechanism for heating gas in the Galactic halo.     

Shock tracers in the molecular cloud G1.6-0.025

Observations of the molecular cloud G1.6-0.025 in the 2_K-1_K and J₀-J_?1E series and 5_?1-4₀E line of CH₃OH, the (2-1) and (3-2) lines of SiO, and the 7_?7-6_?6 line of HNCO are described. Maps of the previously observed extended cloud with V_lsr～50 km/s and high-velocity clump with V_lsr～160 km/s, as well as a newly detected clump with V_lsr～0 km/s, have been obtained. The extended cloud and high-velocity clump have a nonuniform structure. The linewidths associated with all the objects are between 20 and 35 km/s, as is typical of clouds of the Galactic center. In some directions, emission at velocities from 40 to 160 km/s and from ?10 to +75 km/s is observed at the clump boundaries, testifying to a connection between the extended cloud and the high-velocity clump and clump at V_lsr～0 km/s. Compact maser sources are probaby contributing appreciably to the emission of the extended cloud in the 5_?1-4₀E CH₃OH line. Non-LTE modeling of the methanol emission shows that the extended cloud and high-velocity clump have a relatively low hydrogen density (<10⁴ cm^?3). The specific column density of methanol in the extended cloud exceeds 6×10⁸ cm^?3s, and is 4×10⁸?6×10⁹ cm^?3s in the high-velocity clump. The kinetic temperatures of the extended cloud and high-velocity clump are estimated to be <80 K and 150–200 K, respectively. Possible mechanisms that can explain the link between the extended cloud with V_lsr～50 km/s and the clumps with V_lsr～0 km/s and ～160 km/s are briefly discussed.     

Proper motions of open star clusters and the rotation rate of the galaxy

The mean proper motions of 167 Galactic open clusters with radial-velocity measurements are computed from the data of the Tycho-2 catalog using kinematic and photometric cluster membership criteria. The resulting catalog is compared to the results of other studies. The new proper motions are used to infer the Galactic rotation rate at the solar circle, which is found to be ω₀=+24.6±0.8 km s^?1 kpc^?1. Analysis of the dependence of the dispersion of ω₀ estimates on heliocentric velocity showed that even the proper motions of clusters with distances r>3 kpc contain enough useful information to be used in kinematic studies demonstrating that the determination of proper motions is quite justified even for very distant clusters.     

Macromolecules in the galaxy and the cosmic microwave background

A deep search for the predicted Galactic microwave dipole emission of spinning interstellar fullerene-type molecules has been conducted using the RATAN-600 radio telescope. This effect is of interest both in its own right and as a new form of Galactic screen between the cosmic microwave background (CMB) and the observer. The power of this noise component on angular scales of about 0.1° (l=1000) is estimated. These scales are of primary interest for the “Cosmological Gene of the Universe” (RATAN-600), PLANCK Surveyor Mission, and other projects. At the frequencies of the expected emission peak of this dust component, the small-scale noise is a factor of 20 weaker than the predicted noise. It is shown that the role of this dust component is negligible, at least at the main PLANCK frequencies. The first estimates of the contribution from Galactic polarization noise are given for λ=3.9 cm, where the theory predicts a maximum in the CMB polarization (l～1000). At wavelengths of ～1 cm and shorter, macromolecules contribute less than 1 µK, and should not hinder CMB polarization studies. Galactic synchrotron polarization, likewise, should not prevent CMB polarization experiments at the main PLANCK frequencies.     

Structure and kinematics of the interstellar medium near WR 137 and supernova remnants CTB 87 and G73.9+0.9

Using the results of our Hα interferometric observations and observational data on the 21 cm and CO lines, we have analyzed the structure and kinematics of the interstellar medium in the extended vicinity of the star WR 137 and the supernova remnants CTB 87 and G73.9+0.9. A shell structure with a radius of up to 40′ observable in optical lines has been discovered around WR 137. The high-velocity motions of ionized hydrogen inside this shell can be interpreted as expansion of the gas swept out by the wind of WR 137 at velocities of up to 60 km/s. The ionized hydrogen near WR 137 emits at the systematic velocity V _LSR ∼ 6–18 km/s. The expansion ofG73.9+0.9 at a velocity of up to 55 km/s has been confirmed. The systematic velocities of the ionized hydrogen toward this supernova remnant are V _LSR ≃ −14…+14 km/s. An HI shell around G73.9+0.9 has been detected at velocities V _LSR≃−14…−8 km/s. A very faint optical shell of CTB 87 with a size of about 20′ has also been detected. Evidence that CTB 87 is located in the Cygnus Arm is presented.     

The active region Orion KL in polarized emission in the Orion

The fine structure of the active region in the Orion KL gas-dust complex has been measured in polarized H₂O maser emission (epoch December 12, 1998) with an angular resolution of 0.15 mas, or 0.07 AU, and a velocity resolution of 0.05 km/s. The maser emission is concentrated in a line with ΔV = 0.45 km/s, V _LSR = 7.65 km/s, and a flux density of F = 2.1 MJy. The structure consists of a compact source (ejector), highly collimated bipolar outflow, and a toroidal component. The brightness temperature of the ejector is T _b = 2 × 10¹⁶ K, and its degree of linear polarization reaches m ≈ 20%. The variation of the polarization angle across the profile is dX/dV = ?23°/(km/s), which considerably exceeds the Faraday rotation in the HII region foreground to the molecular cloud. The observed “rotation” is explained as an effect of different orientations for the polarization of the ejected outflows. The brightness temperature of the bipolar outflow is T _b ≈ 10¹⁴ K, while that of individual components is T _b ≈ 10¹⁵ K. The degree of polarization in the components exceeds that of the ejector and reaches m ≈ 50%. The position angle of the polarization is X ≈ 45° relative to the outflow. The torus, which is observed edge-on, has a diameter of 0.38 AU and a thickness of 0.08 AU. The brightness temperature of the tangential directions in the torus is T _b ≈ 5 × 10¹⁵ K, and the rotational velocity is V _rot ≈ 0.02 km/s. The degree of polarization is m ≈ 40%, and its position angle relative to the azimuthal plane is X ≈ 43°. The relative deviations of the polarization plane in the bipolar outflow and torus relative to the pumping direction are nearly the same and are determined by Faraday rotation within the HII region.     

The bulk motion of FGC galaxies on scales of 100 Mpc

Large-scale streaming is analyzed using a sample of 983 thin, edge-on galaxies from the FGC catalog with radial velocities cz<18000 km s^?1. The catalog covers the entire sky and contains galaxies with apparent axial ratios a/b>7 and angular diameters a>0.6 arcmin. The distances to the galaxies were determined using a multi-parameter “rotation amplitude-linear diameter” relation, which is similar to the Tully-Fisher relation and takes into account surface brightness, morphological type, and other global parameters. The bulk motion of the galaxy sample with respect to the frame of the microwave background radiation can be described by a dipole solution with amplitude V ^B =300±75 km s^?1 in the direction (l=328°, b=+7°)±15°. The apex parameters for the FGC galaxies agree well with the amplitude and direction of the bulk motion for the Mark III compiled catalog, although the two samples have no objects in common. The dipole solution provides only a rough approximation to the smoothed peculiar-velocity field of the FGC galaxies. Areas of maxima and minima on the V _pec map are not correlated with the locations of known nearby clusters and voids. A comparison of nearby and distant subsamples shows that the amplitude of the bulk motion with respect to the 3K reference frame does not decrease with distance. The observed large-scale galaxy streaming could be due to the Shapley concentration of rich clusters (311°, +30°), which is located within 2σ of the apex.     

Measurements of the scattering of pulsar radio emission

Measurements of the broadening of pulsar pulses by scattering in the interstellar medium are presented for a complete sample of 100 pulsars with Galactic longitudes from 6° to 311° and distances to three kiloparsec. The dependences of the scattering on the dispersion measure (τ _sc(DM) ∝ DM^α), frequency (τ _sc(v) ∝ v ^?γ ), Galactic longitude, and distance to the pulsar are analyzed. The dependence of the scattering on the dispersion measure in the near-solar neighbourhood can be represented by the power law τ _sc(DM) ∝ DM^2.2±0.1). Measurements at the low frequencies 111, 60, and 40 MHz and literature data are used to derive the frequency dependence of the scattering (τ _sc(v) ∝ V ^?γ ) over a wide frequency interval (covering a range of less than 10: 1) with no fewer than five frequencies. The index for the frequency dependence, γ = 4.1 ± 0.3, corresponds to a normal distribution for inhomogeneities in the turbulence in the scattering medium. Based on an analysis of the dependence of the scattering on the distance to the pulsar and on Galactic longitude, on average, the turbulence level C _n ² is the same in all directions and at all distances out to about three kpc, testifying to the statistical homogeneity of the turbulence of the scattering medium in the near-solar region of the Galaxy.     

Peculiarities of α-element abundances in Galactic open clusters

A catalog compiling the parameters of 346 open clusters, including their metallicities, positions, ages, and velocities has been composed. The elements of the Galactic orbits for 272 of the clusters have been calculated. Spectroscopic determinations of the relative abundances, [el/Fe], for 14 elements synthesized in various nuclear processes averaged over data from 109 publications are presented for 90 clusters. The compiled data indicate that the relative abundances of primary α elements (oxygen and magnesium) exhibit different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits in clusters with high, elongated orbits satisfying the criterion (Z_max² + 4e²)^1/2 > 0.40 and in field stars of the Galactic thin disk (Z_max is the maximum distance of the orbit from the Galactic plane in kiloparsec and e is the eccentricity of the Galactic orbit). Since no systematic effects distorting the relative abundances of the studied elements in these clusters have been found, these difference suggest real differences between clusters with high, elongated orbits and field stars. In particular, this supports the earlier conclusion, based on an analysis of the elements of the Galactic orbits, that some clusters formed as a result of interactions between high-velocity,metal-poor clouds and the interstellar mediumof theGalactic thin disk. On average, clusters with high, elongated orbits and metallicities [Fe/H] < -0.1 display lower relative abundances of the primary a elements than do field stars. The low [O, Mg/Fe] ratios of these clusters can be understood if the high-velocity clouds that gave rise to them were formed of interstellar material from regions where the star-formation rate and/or the masses of Type II supernovae were lower than near the Galactic plane. It is also shown that, on average, the relative abundances of the primary a elements are higher in relatively metal-rich clusters with high, elongated orbits than in field stars. This can be understood if clusters with [Fe/H] > -0.1 formed as a result of interactions between metal-rich clouds with intermediate velocities and the interstellar medium of the Galactic disk; such clouds could form from returning gas in a so-called “Galactic fountain.”     

Galactic orbits of selected companions of the Milky Way

High-accuracy absolute proper motions, radial velocities, and distances have now been measured for a number of dwarf-galaxy companions of the Milky Way, making it possible to study their 3D dynamics. Galactic orbits for 11 such galaxies (Fornax, Sagittarius, Ursa Minor, LMC, SMC, Sculptor, Sextans, Carina, Draco, Leo I, Leo II) have been derived using two previously refined models for the Galactic potential with the Navarro–Frenk–White and Allen–Santillán expressions for the potential of the dark-matter halo, and two different masses for the Galaxy within 200 kpc—0.75 × 10¹² M _⊙ and 1.45 × 10¹² M _⊙. The character of the orbits of most of these galaxies indicates that they are tightly gravitationally bound to the Milky Way, even with the lower-mass model for the gravitational potential. One exception is the most distant galaxy in the list, Leo I, whose orbit demonstrates that it is only weakly gravitationally bound, even using the higher-mass model of the gravitational potential.     

The accretion activity of the Ae Herbig star CQ Tau

Results of spectral observations of the isolated Ae Herbig star CQ Tau obtained in 1995–1998 in the H_α line and near the sodium resonance doublet are presented, together with simultaneous photometric monitoring of the star. CQ Tau is a member of the family of young UX Ori stars with nonperiodic Algol-like brightness decreases. The star is surrounded by an accretion disk, in which its emission-line spectrum and part of its absorption-line spectrum are formed. The strong variability of the H_α, D NaI, and HeI 5876 Å lines testifies that the gaseous disk is appreciably inhomogeneous in both the radial and azimuthal directions. This inhomogeneity probably results from uneven feeding by the circumstellar material from the peripheral regions of the circumstellar disk. Over the four years of observations, we observed the star in deep minima three times (ΔV～2). On these nights, an increase in the H_α equivalent width followed the decrease in radiation flux. In the two deepest minima, the normally two-component line profile had only a single component with a nearly symmetrical profile. This behavior of the H_α line is in good agreement with the results of numerical modeling of Algol-like minima and can be used to estimate the parameters of the dust clouds eclipsing the star and inner accretion disk. These estimates suggest that the circumstellar dust clouds can approach very close to the star and be sublimated there.     

Physical properties of molecular clouds as functions of their Galactocentric distance from CS and C<Superscript>34</Superscript>S observations

Twenty-eight CS molecular clouds toward HII regions with Galactocentric distances from ～ 4 to 20 kpc have been studied based on observations obtained in the J=2→1 lines of CS and C³⁴S on the 20-meter radio telescope of the Onsala Space Observatory (Sweden) in March 2001. All 28 clouds have been mapped with an angular resolution of ～40″. The peak intensity in the C³⁴S line has been measured for 20 objects. An LTE analysis has been performed and the parameters of the molecular cloud cores derived. The core sizes are d_A=0.3–4.8 pc, with a median value of ～1.6 pc. The mean hydrogen densities in the cloud cores are n_H2=3.5×10²–3.7 × 10⁴ cm^?3, with a median value of ～7.2×10³ cm^?3. The value of n_H2 ends to decrease with increasing Galactocentric distance of the cloud. The masses of most clouds are 10²?6×10³M_⊙, with the most probable value being M_CS～10³M_⊙. The data follow the dependence M_CS ∝d _A ^(2.4–3.2) . As a rule, the cloud masses are lower than the virial masses for M_CS<10³M_⊙.     

V1327 Aquilae: A New RR Lyrae variable with an extremely high radial velocity

We have carried out photometry and spectroscopy of the star V1327 Aql (R = 16 ^m ) as part of our program of observations of poorly studied cataclysmic variables using the 1.5-m optical Russian—Turkish telescope (RTT-150, Turkey) and the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. After analyzing our photometry, we have re-classified the variable as an RR Lyrae star. Our BV R photometry during 10 nights reveals brightness variations with the period 12^h49^m, with the B, V, and R amplitudes being 1.36 ^m , 1.13 ^m , and 1.11 ^m , respectively. We derived the first estimates of the star’s atmospheric parameters from our moderate-resolution spectra: T _eff = 6280 K, log g = 3.3, [M/H] = ?1.05. The extremely high radial velocity of the star’s motion (V _R = ?470 km/s) and the star’s large distances to the Galactic center (13.1 kpc) and disk (4.2 kpc) testify to a probable extragalactic origin of this object.     

Formation of a protoplanetary system through the merging of binary components that are contracting towards the main sequence

We have carried out three-dimensional hydrodynamical modeling of the formation of planets through the merging of a binary system comprised of low-mass (～0.5–1 M_⊙) stars in the stage of contracting towards the main sequence. Under certain conditions, the disruption of the more massive component results in the formation of an expanding disk and extended arm. The fragmentation of this arm leads to the formation of planetary-mass clouds (<5 M _J where M _J is the mass of Jupiter), whose orbits can have semimajor axes of 0.4 to 5 AU and substantial (～0.5) eccentricities.