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We present a dynamics study toward the G326.611+0.811 (G326) hub–filament system (HFS) cloud using new APEX observations of both 13CO and C18O (J = 2–1). The G326 HFS cloud constitutes a central hub and at least four hub-composing filaments that are divided into a major branch of filaments (F1 and F2) and a side branch (F3–F5). The cloud holds ongoing high-mass star formation as characterized by three massive dense clumps (i.e., 370–1100 M ⊙ and 0.14–0.16 g cm−2 for C1–C3) with high clump-averaged mass infalling rates (>10−3 M ⊙ yr−1) within the major filament branch, and the associated point sources bright at 70 μ m, typical of young protostars. Along the five filaments, velocity gradients are found in both 13CO and C18O (J = 2–1) emission, suggesting that filament-aligned gravitational collapse toward the central hub (i.e., C2) is responsible for the high-mass star formation therein. Moreover, a periodic velocity oscillation along the major filament branch is revealed in both 13CO and C18O (J = 2–1) emission with a characteristic wavelength of ∼3.5 pc and an amplitude of ∼0.31–0.38 km s−1. We suggest that this pattern of velocity oscillation in G326 could arise from clump-forming gas motion induced by gravitational instabilities. The prevalent velocity gradients, fragmentation of the major branch of filaments, and the ongoing collapse of the three massive dense clumps are indicative that G326 is an HFS undergoing global collapse. [ABSTRACT FROM AUTHOR]

Because of detailed monitoring of the 22.2 GHz water maser, carried out from 2021 October to 2023 May, a very powerful flare phenomenon was detected in the galactic object W51 near the radial velocity of 60 km s−1 with the amplitude of 140 kJy. A phenomenon of this magnitude was unprecedented in the entire history of observations of the source. Eleven short flares were recorded. The exponential increase and decrease in the flare flux density while reducing in their spectral line widths indicated that water masers were in an unsaturated state during the flares. All flares were located at the top of the less powerful Flare 0 with the amplitude of 13.5 kJy and the spectral line half-width of 3.0 km s−1. Such a wide line of the water maser, as well as the amplitude, of the flare phenomenon are so far unique discoveries. The water maser of Flare 0 may have been saturated and created a significant input flux density for other flares of this phenomenon. The extremely high density of maser spots in a cluster led to their partial overlap on the observer's line of sight. This also confirmed the hypothesis about the need for a significant length of the path along which the generation of maser radiation occurs. New parameters of water masers and the most important physical conclusions have been obtained. The possibility of detecting gravitational waves from massive binary stars at the stage of evolution close to merging is considered for the case of W51 Main. [ABSTRACT FROM AUTHOR]

Using optical photometric observations from 1.3-m Devasthal Fast Optical Telescope and deep near-infrared (NIR) photometric observations from TANSPEC mounted on 3.6-m Devasthal Optical Telescope, along with the multi-wavelength archival data, we present our study of open cluster Kronberger 55 to understand the star-formation scenario in the region. The distance, extinction and age of the cluster Kronberger 55 are estimated as ∼ 3.5 kpc, E (B - V) ∼ 1.0 mag and ≲ 5 Myr, respectively. We identified Young Stellar Objects (YSOs) based on their excess infrared (IR) emission using the two-color diagrams (TCDs). The mid-infrared (MIR) images reveal the presence of extended structure of dust and gas emission along with the outflow activities in the region with two peaks, one at the location of cluster Kronberger 55 and another at 5 ′. 35 southwards to it. The association of radio continuum emission with the southern peak, hints towards the formation of massive star/s. The Herschel sub-millimeter maps reveal the presence of two clumps connected with a filamentary structure in this region, and such configuration is also evident in the 12 CO(1–0) emission map. Our study suggests that this region might be a hub-filament system undergoing star formation due to the 'end-dominated collapse scenario'. [ABSTRACT FROM AUTHOR]

The radiation from stars and active galactic nuclei (AGNs) creates photodissociation regions (PDRs) and X-ray-dominated regions (XDRs), where the chemistry or heating is dominated by far-ultraviolet (FUV) radiation or X-ray radiation, respectively. PDRs include a wide range of environments, from the diffuse interstellar medium (ISM) to dense star-forming regions. XDRs are found in the center of galaxies hosting AGNs, in protostellar disks, and in the vicinity of X-ray binaries. In this review, we describe the dominant thermal, chemical, and radiation transfer processes in PDRs and XDRs, as well as give a brief description of models and their use for analyzing observations. We then present recent results from Milky Way, nearby extragalactic, and high-redshift observations. Several important results include the following: Velocity-resolved PDR lines reveal the kinematics of the neutral atomic gas and provide constraints on the stellar feedback process. Their interpretation is, however, in dispute, as observations suggest a prominent role for stellar winds, whereas they are much less important in theoretical models. A significant fraction of molecular mass resides in CO-dark gas especially in low-metallicity and/or highly irradiated environments. The CO ladder and [Ci]/[Cii] ratios can determine if FUV or X rays dominate the ISM heating of extragalactic sources. With Atacama Large Millimeter/submillimeter Array, PDR and XDR tracers are now routinely detected on galactic scales over cosmic time. This makes it possible to link the star-formation history of the Universe to the evolution of the physical and chemical properties of the gas. [ABSTRACT FROM AUTHOR]

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]

Non-thermal particles and high-energy radiation can play a role in the dynamical processes in star-forming regions and provide an important piece of the multiwavelength observational picture of their structure and components. Powerful stellar winds and supernovae in compact clusters of massive stars and OB associations are known to be favourable sites of high-energy particle acceleration and sources of non-thermal radiation and neutrinos. Namely, young massive stellar clusters are likely sources of the PeV (petaelectronvolt) regime cosmic rays (CRs). They can also be responsible for the cosmic ray composition, e.g., 22Ne/20Ne anomalous isotopic ratio in CRs. Efficient particle acceleration can be accompanied by super-adiabatic amplification of the fluctuating magnetic fields in the systems converting a part of kinetic power of the winds and supernovae into the magnetic energy through the CR-driven instabilities. The escape and CR propagation in the vicinity of the sources are affected by the non-linear CR feedback. These effects are expected to be important in starburst galaxies, which produce high-energy neutrinos and gamma-rays. We give a brief review of the theoretical models and observational data on high-energy particle acceleration and their radiation in star-forming regions with young stellar population. [ABSTRACT FROM AUTHOR]

Massive stars, from birth to death, play a vital role in our Universe. Characteristically, massive stars (M_ZAMS > 8M_0) bum bright and die young. Their spectacular deaths lead to core-collapse Supernovae which enrich the Universe with lighter metals like carbon and oxygen, leave black holes or neutron stars as remnants, and produce gravitational waves. Massive stars tend to be in binary systems of two or more stars with 90% of massive stars having one or more companions. We utilized the high spatial resolution imaging techniques of SPHERE in order to resolve milliarcsecond binary systems with contrast ratios of up to 10 mag in the infrared and detect stellar companions to massive stars in the subsolar mass ranges. We employed IRDIS and IFS to simultaneously capture dual-band imaging and spectroscopy of seven massive stars (ranging from O4V - O9V) in Ml7. Preliminary inspections find that four out of seven targets have a companion with angular separations of 0.1" -- 0.5". With SPHERE, we observe low-mass companions to massive stars that may still be forming and expand the general understanding of binary systems for all mass ratios. [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]

The discovery of large numbers of young low-mass stars and brown dwarfs over the past decade has made it possible to investigate star formation and early evolution in a previously unexplored mass regime. In this review, we begin by describing surveys for low-mass members of nearby associations, open clusters, star-forming regions, and the methods used to characterize their stellar properties. We then use observations of these populations to test theories of star formation and evolution at low masses. For comparison to the formation models, we consider the initial mass function, stellar multiplicity, circumstellar disks, protostellar characteristics, and kinematic and spatial distributions at birth for low-mass stars and brown dwarfs. To test the evolutionary models, we focus on measurements of dynamical masses and empirical Hertzsprung-Russell diagrams for young brown dwarfs and planetary companions. [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]

Magnetic field strengths and directions can be estimated using many different observational techniques that span a wide range of wavelengths. Each observational method favours different regimes of scale size, density and other physical conditions. The available techniques and their ranges of applicability are briefly described and the current status of observations is reviewed, with particular emphasis on high-resolution observations of star-forming regions. [ABSTRACT FROM AUTHOR]