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The collisional pumping of H O and СH OH masers in magnetohydrodynamic nondissociative C-type shocks is considered. A grid of C-type shock models with speeds in the range 5–70 km s and preshock gas densities – cm is constructed. The large velocity gradient approximation is used to solve the radiative transfer equation in molecular lines. The para-H O 183.3 GHz and ortho-H O 380.1 and 448.0 GHz transitions are shown to be inverted and to have an optical depth along the shock velocity at relatively low gas densities in the maser zone, – cm . Higher gas densities, cm , are needed for efficient pumping of the remaining H O masers. Simultaneous generation of H O and class I СH OH maser emission in a shock is possible at preshock gas densities cm and shock speeds in the range km s . The possibility of detecting class I СH OH and para-H O 183.3 GHz masers in star-forming regions and near supernova remnants is investigated. [ABSTRACT FROM AUTHOR]

Based on published data, we have produced a sample of 256 radio sources whose trigonometric parallaxes and proper motions were measured by VLBI. This sample contains Galactic masers associated with massive protostars and stars in active star-forming regions. It also includes young low-mass stars from the Gould Belt region whose radio observations were performed in continuum. Based on this, most complete sample of sources to date, we have estimated the velocities , , and the parameters of the angular velocity of Galactic rotation and obtained a new estimate of the distance from the Sun to the Galactic center, kpc. The parameters of the Galactic spiral density wave have been found from the series of radial, , and residual tangential, , velocities of stars. The amplitudes of the radial and tangential velocity perturbations are km s and km s , the perturbation wavelengths are kpc and kpc, and the Sun's phases in the spiral density wave are and for the adopted four-armed spiral pattern. [ABSTRACT FROM AUTHOR]

We have studied a sample of more than 25 000 young stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The relative errors of their parallaxes do not exceed 10 . The selection of stars belonging to active star-forming regions was made by Marton et al. based on data from the Gaia DR2 catalogue by invoking infrared measurements from the WISE and Planck catalogues. Low-mass T Tauri stars constitute the majority of sample stars. The following parameters of the angular velocity of Galactic rotation have been found from them: km s kpc , km s kpc , and km s kpc . The Oort constants are km s kpc and km s kpc , while the circular rotation velocity of the solar neighborhood around the Galactic center is km s for the adopted Galactocentric distance of the Sun kpc. [ABSTRACT FROM AUTHOR]

We present the results of our long-term monitoring of the 1.35-cm water-vapor maser source ON 1 performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory from 1981 to 2013. Maser emissionwas observed in a wide range of radial velocities, from −60 to +60 km s. Variability of the integrated flux with a period of ∼9 years was detected. We show that the stable emission at radial velocities of 10.3, 14.7, and 16.5 km s belongs to compact structures that are composed of maser spots with close radial velocities and that are members of two water-maser clusters, WMC 1 and WMC 2. The detected short-lived emission features in the velocity ranges from −30 to 0 and from 35 to 40 km s as well as the high-velocity ones are most likely associated with a bipolar molecular outflow observed in the CO line. [ABSTRACT FROM AUTHOR]

The effect of quasi-resonance energy transfer in collisions between H and HO molecules in HO maser sources is investigated. New data on the state-to-state rate coefficients for collisional transitions for HO and H molecules are used in the calculations. The results of ortho-HO level population inversion calculations for the 22.2-, 380-, 439-, and 621-GHz transitions are presented. The ortho-HO level population inversion is shown to depend significantly on the population distribution of the para-H J = 0 and 2 rotational levels. The possibility of quasi-resonance energy transfer in collisions between H molecules at highly excited rotational-vibrational levels and HO molecules is considered. The quasi-resonance energy transfer effect can play a significant role in pumping HO masers in the central regions of active galactic nuclei and in star-forming regions. [ABSTRACT FROM AUTHOR]

A detailed photometric study of star-forming regions (SFRs) in the galaxy Holmberg II has been carried out using the archival observational data from the far infrared to the ultraviolet obtained with the GALEX, Spitzer, and Herschel telescopes. Spectroscopic observations with the 6-m BTA telescope (Special Astrophysical Observatory of the Russian Academy of Sciences) are used to estimate the ages and metallicities of SFRs. The ages of SFRs have been correlated for the first time with their emission parameters in a wide spectral range and with the physical parameters determined by fitting the observed spectra. It is shown that the fluxes at 8 and 24 µm characterizing the emission from polycyclic aromatic hydrocarbons (PAHs) and hot dust grains decrease with age, but their ratio increases. This implies that the relative contribution from PAHs to the total infrared flux increases with age. It is hypothesized that the detected increase in the ratio of the fluxes at 8 and 24 µm is related to the increase in the relative PAH fraction due to the destruction of larger grains. [ABSTRACT FROM AUTHOR]

We have tested the method of determining the solar Galactocentric distance R and Galactic rotation velocity V modified by Sofue et al. using near-solar-circle objects. The motion of objects relative to the local standard of rest has been properly taken into account. We show that when such young objects as star-forming regions or Cepheids are analyzed, allowance for the perturbations produced by the Galactic spiral density wave improves the statistical significance of the estimates. The estimate of R = 7.25 ± 0.32 kpc has been obtained from 19 star-forming regions. The following estimates have been obtained from a sample of 14 Cepheids (with pulsation periods P > 5): R = 7.66 ± 0.36 kpc and V = 267 ± 17 km s. We consider the influence of the adopted Oort constant A and the character of stellar proper motions (Hipparcos or UCAC4). The following estimates have been obtained from a sample of 18 Cepheids with stellar proper motions from the UCAC4 catalog: R = 7.64 ± 0.32 kpc and V = 217 ± 11 km s. [ABSTRACT FROM AUTHOR]

Polarization observations of the HO maser emission at 1.35 cm from the active region Orion KL were carried out at epoch 2011.7 on the Svetloe-Zelenchukskaya radio interferometer. The observational data have been processed on the correlator of the QUASAR network. Fragments of the structure have been identified; the line velocities and profile widths and the emission polarization have been determined. The component at the radial velocity V = 7.0 km s has been taken as a reference one. Its effective size in the Gaussian approximation is 1.5 mas, the axial ratio is Major/Minor = 3.3, and the orientation is PA = 11°. The component V = 7.6 km s corresponds to a bipolar outflow with an effective size of 6.2 mas, the axial ratio is Major/Minor = 5.3, and the orientation −32°. The bipolar outflow is 10 mas away from the reference feature in the direction of 173°. The longitudinal velocity components of the NW and SE parts of the bipolar outflow in the local standard of rest are +0.15 and −0.15 km s, respectively. The degrees of polarization of the emission from the reference feature (7.0 km s) and the bipolar outflow are m = 39 and 52%, respectively. The difference in polarization orientations of both components Δ does not exceed 3°. [ABSTRACT FROM AUTHOR]

The collisional pumping of HO and HO masers in hot dense gas-dust clouds has been simulated numerically. New data on the rate coefficients for collisional transitions from Faure et al. (2007) were used in the calculations. The possibility of detecting HO emission in 22.2-GHz HO maser sources is investigated. The medium is shown to become optically thick in the HO lines for which an inverted level population is observed at HO column densities of ∼1019-1020 cm. A simultaneous observation of HO emission and HO maser emission in the same source will allow the physical conditions in the gas-dust cloud to be refined. [ABSTRACT FROM AUTHOR]

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, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives. For R = 8 kpc, we have found the circular velocity of the Sun to be V = 243 ± 16 km s, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s kpc and B = −13.5 ± 1.4 km s kpc. 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) depend significantly on the Sun's phase in the spiral wave. [ABSTRACT FROM AUTHOR]

We present the observations of the Irr galaxy IC 10 at the 6-m SAO telescope with the panoramic Multi-Pupil Fiber Spectrograph (MPFS). Based on the results of these observations and our long-slit spectroscopy performed previously, we have investigated the ionized-gas emission spectrum in the region of intense star formation and refined the gas metallicity estimates. We show that the 'diagnostic diagrams' constructed from our observations agree best with the new improved ionization models by Martin-Manjon et al. Using these models, we have determined the electron density and gas ionization parameter and ionizing-cluster characteristics, the age and mass, from the spectra of the investigated HII regions. The cluster ages and masses are shown to be within the ranges 2.5-5 Myr and (0.2-1) × 10 M, respectively. [ABSTRACT FROM AUTHOR]

A comparative analysis of the evolution of integrated photometric parameters for young star formation complexes in spiral and irregular galaxies and open star clusters in our Galaxy is performed. Extragalactic star formation complexes seen as giant H II regions and open star clusters in the Milky Way are shown to represent a single evolutionary sequence of objects at different stages of their evolution when the extinction is properly taken into account. [ABSTRACT FROM AUTHOR]

Based on currently available data on the three-dimensional field of space velocities of young (≤50 Myr) open star clusters and the radial velocities of HI clouds and star-forming (H II) regions, we have found the Galactic rotation curve in the range of Galactocentric distances 3 kpc < R < 12 kpc using the first six terms of the Taylor expansion of the angular velocity of Galactic rotation in Bottlinger’s equations. The Taylor terms found at the Galactocentric distance of the Sun R 0 = 7.5 kpc are: ω 0 = −27.7 ± 0.6 km s−1 kpc−1, ω = 4.13 ± 0.07 km s−1 kpc−2, ω = −0.912 ± 0.065 km s−1 kpc−3, ω = 0.277 ± 0.036 km s−1 kpc−4, ω = −0.265 ± 0.034 km s−1 kpc−5, ω = 0.104 ± 0.020 km s−1 kpc−6. In this case, the Oort constants are A = 15.5 ± 0.3 km s−1 kpc−1 and B = −12.2 ± 0.7 km s−1 kpc−1. We have established that the centroid of the sample moves relative to the local standard of rest along the Galactic Y axis with a velocity of −6.2 ± 0.8 km s−1. A Fourier spectral analysis of the velocity residuals from the derived rotation curve attributable to density waves reveals three dominant peaks with wavelengths of 2.5, 1.4, and 0.9 kpc and amplitudes of 4.7, 2.6, and 3.6 km s−1, respectively. These have allowed us to estimate the distances between the density wave peaks, 1.9, 2.4, and 3.2 kpc as R increases, in agreement with the description of the density weave as a logarithmic spiral. The amplitude of the density wave perturbations is largest in the inner part of the Galaxy, ≈9 km s−1, and decreases to ≈1 km s−1 in its outer part. A spectral analysis of the radial velocities of young open star clusters has confirmed the presence of periodic perturbations with an amplitude of 5.9 ± 1.1 km s−1 and a wavelength λ = 1.7 ± 0.5 kpc. It shows that the phase of the Sun in the density wave is close to − π/2 and the Sun is located in the interarm space near the outer edge of the Carina-Sagittarius arm. [ABSTRACT FROM AUTHOR]

We consider the effects of the grain size, shape, structure, and chemical composition as well as the angle between the grain rotation axis and the incident ray on the full widths at half maximum (FWHM) of the polarization bands in the two deepest infrared absorption bands observed in the spectra of protostars, the water-ice band centered at 3.1 μm and the silicate band centered at 9.7 μm, using a core—mantle confocal spheroid model with various axial ratios a/b and relative volumes of the core material. We have found that the observed polarization bands with FWHMp < 0.3 μm in the water-ice absorption band can be explained only by oblate and prolate particles with r v ≤ 0.35 μm and the polarization bands with FWHMp ≈ 0.3 μm can be explained only by particles with r v ≈ 0.35 μm. Broad silicate absorption bands (FWHM ≈ 3 μm) with broad polarization bands (FWHMp ≈ 2.7 μm) can be explained by particles with r v ≈ 0.35 μm. Narrow silicate absorption bands (FWHM ≤ 3 μm) with any FWHM of the polarization bands can be explained by a mixture of particles of two types of olivine. Narrow polarization bands (FWHMp ≈ 2 μm) with broad absorption bands can be explained only by very small particles, r v ≤ 0.1 μm. We have found the relationships between the effective polarization and extinction cross sections and estimated the ranges of observed polarizabilities that can be explained by particles of given shape and orientation in each of the bands independently. Independent studies of the observational data for each of the bands are shown to give a wider choice of particle model parameters. [ABSTRACT FROM AUTHOR]

We investigate the linear polarization in the two deepest infrared absorption bands observed in the spectra of protostars, the water-ice band with the center near 3.1 µm and the silicate band with the center near 9.7 µm, using a core-mantle confocal spheroid model with various axial ratios a/b and relative volumes of the core material. We consider the effect of the grain shape, structure, and type (oblate, prolate) as well as the type of grain orientation and its location relative to the incident ray of light and the magnetic field direction on the central wavelengths of the two bands and the polarizability in the bands. We have found that the observed relationships between the polarizability in the bands and the ratio of their optical depths at the band centers can be explained if we choose slightly oblate or prolate particles ( a/b ≲2 for the silicate band and 1.3 ≲ a/b ≲ 2 for the ice band). For any type of orientation, the core-mantle confocal spheroid model requires different axial ratios for the ice and silicate bands to account for the observed polarization. We show that picket-fence-oriented particles can explain the observed polarization in the ice band at angles α between the particle rotation axis and the incident ray ≳30° and in the silicate band at any α. Perfectly Davis-Greenstein-oriented particles can explain the observed polarization in the ice band at angles Ω between the line of sight and the magnetic field direction ≳60° and in the silicate band at any Ω. The orientation parameter ζ (imperfect Davis-Greenstein orientation) must be no more than 0.5 (oblate particles) and 0.1 (prolate particles) for the ice band and can be arbitrary for the silicate band. [ABSTRACT FROM AUTHOR]