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1.
W75N is a star-forming region containing ultracompact H II regions as well as OH, H2O, and methanol masers. The VLBA maps obtained show that the masers are located in a thin disk rotating around an O star, which is the exciting star for the ultracompact H II region VLA1. A separate group of maser spots is associated with the ultracompact H II region VLA2. The radial velocity of the maser spots varies across the disk from 3.7 to 10.9 km/s. The disk diameter is 4000 AU. The maser spots revolve in Keplerian orbits around the O9 star. 相似文献
2.
We present the results of studies of the superfine structure of H2O maser sources in the Orion Nebula. Powerful, low-velocity, compact maser sources are distributed in eight active zones. Highly organized structures in the form of chains of compact components were revealed in two of these, in the molecular cloud OMC-1. The component sizes are ～0.1 AU and their brightness temperatures are T b =1012?1016 K. The structures correspond to tangential sections of concentric rings viewed edge-on. The ring emission is concentrated in the azimuthal plane, decreasing the probability of their discovery. The formation of protostars is accompanied by the development of accretion disks and bipolar flows, with associated H2O maser emission. The accretion disks are in the stage of fragmentation into protoplanetary rings. In a Keplerian approximation, the protostars have low masses, possibly evidence for instability of the systems. Supermaser emission of the rings is probably triggered by precession of the accretion disk. The molecular cloud’s radial velocity is V LSR=7.74 km/s and its optical depth is τ≈5. The emission from components with velocities within the maser window is additionally amplified. The components’ emission is linearly polarized via anisotropic pumping. 相似文献
3.
The paper presents the results of monitoring the H2O maser in NGC 7538, which is associated with a star-formation region, in 1993–2003. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia). The variability of the maser emission displays a cyclic character. Two cycles of the long-term variability of the total flux were detected over the entire monitoring period (1981–2003): 1981–1993 and 1994–2003. The period of the variability is about 13 years. An anticorrelation of the emission in lateral sections of the spectra is observed, as is characteristic of protoplanetary disks. A drift in the radial velocity of the central component is observed (VLSR=?60 km/s) with a drift rate of about 0.09 km/s per year. The water-vapor maser is most likely associated with a protoplanetary disk. 相似文献
4.
Results of a multi-faceted study of the H2O maser emission in the region ON2 N carried out on the Very Large Array (VLA, NRAO) and 22-m radio telescope of the Pushchino
Radio Astronomy Observatory are reported. The envelope around the ultracompact HII region is fairly extended and has a composite,
strongly fragmented structure. The maser emission zone consists of single spots and spot clusters arranged along an arc, which
is associated with a ram shock front. This shock front is nonsta-tionary, and its position changes with time. The front position
probably depends on the state of activity of the central star. There can be turbulent motions of material in clusters as well
as individual maser spots (such as turbulent vortices). In the turbulent-vortex model, the size of an H2O maser spot is estimated to be 0.07–0.1 AU. Flux-correlated radial-velocity drifts of emission features have been detected,
which can be accompanied by spatial displacement (proper motion) of maser spots. 相似文献
5.
P. Colom E. E. Lekht M. I. Pashchenko G. M. Rudnitskii A. M. Tolmachev 《Astronomy Reports》2018,62(7):440-454
The results of a study of H2O and OH maser emission in the complex region of active star formation W75 N are presented. Observations were obtained using the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) and the Nan3ay radio telescope (France). Flaring H2O maser features may be identified with maser spots associated with the sources VLA 1 and VLA 2. Themain H2O flares occurred in VLA 1. The flare emission was associated with either maser clusters having closely spaced radial velocities and sizes up to ~2 AU or individual features. The maser emission is generated in a medium where turbulence on various scales is present. Analysis of the line shapes during flare maxima does not indicate the presence of the simplest structures—homogeneous maser condensations. Strong variability of the OH maser emission was observed. Zeeman splitting of the 1665-MHz line was detected for several features of the same cluster at a radial velocity of +5.5 km/s. The mean line-of-sight magnetic field in this cluster is ~0.5 mG, directed away from the observer. Flares of the OH masers may be due to gas compression at a shock or MHD wave front. 相似文献
6.
We present the results of a variability study of some H2O maser-emission components of Sgr B2, which is located in an active star-forming region. Our monitoring was conducted in 1982–2004 with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. We analyze brightness variations for the strongest groups of emission features in the H2O spectra, mainly during periods of maser flaring activity. Each of these groups contains many components, whose radial velocities and fluxes we determined. Most of the components displayed radial-velocity drifts. We detected a correlation between the flux and radial-velocity variations for some of the components. Variability of the emission can be explained in a model in which the maser spots form elongated chains and filaments with radial-velocity gradients. During H2O flares, the flux increases of some maser spots were accompanied by acceleration, while flux decreases were accompanied by deceleration of their motion in the dense circumstellar matter. Spectral groups of emission features are probably spatially compact structures. 相似文献
7.
An analysis of the H2O maser emission toward the source NGC 7538N, which is associated with an active star-forming region, is reported. The analysis is based on 24 years of monitoring in the 1.35-cm line using the the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 1981–2005 with a spectral resolution of 0.101 km/s. Individual spectral components have been isolated, and temporal drifts in their radial velocities found. From time to time, the drifts were accompanied by velocity jumps. This can be explained if there are chains consisting of clumps of material that are elongated in the radial direction toward the star and have a radial-velocity gradient. In 1982–2005, two maser activity cycles were observed, during which the chains were activated. We propose that shocks consecutively cross the chain elements and excite maser emission in them. The longest chain, at a radial velocity of ?58 km/s, has not fewer than 15 links. For a shock velocity of 15 km/s, the chain step is estimated to be ≤1.5 AU. The chains could be located in a circumstellar disk with a width of ≤1015 cm. A structure in the form of a rotating nonuniform vortex with the rotation period of about 1.6 years has also been detected. The translational motion of the vortex may be a consequence of its orbital motion within the protoplanetary disk. 相似文献
8.
We have carried out detailed studies of a star-forming region containing two maser sources in the constellation Norma. The sources display a complex spectral distribution of the maser lines and spatial distribution of the maser condensations. The maser condensations may have formed around objects that are hidden by dense molecular cocoons; the velocities of the maser features may represent Keplerian orbital motions. The cocoons, which radiate in thermal methanol and CS lines, correspond to the centers of mass in the maser sources + dense molecular core systems. The velocities of the CS lines or thermal methanol lines can be used to identify the locations of the centers of mass of these systems. If the maser radiation is generated in the atmospheres of protoplanets, the Norma radio source may correspond to two protoplanetary disks, each with a protostar and protoplanetary system. In this case, the masses of the protostars are approximately 13 M⊙ and 38 M⊙. 相似文献
9.
A model of the source associated with VLA 1 in W75N is constructed based on monitoring of the H2O maser carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory and NRAO VLA maps of the source at epochs 1992, 1996, 1998, and 1999. The source has a complex hierarchical structure. Individual maser spots form compact clusters in the form of filaments or chains, as well as more extended arc-like clusters. There are radial-velocity gradients in the chains and filaments. All these structures are arranged in a very elongated disk. This complex configuration could arise due to various-scale turbulent motions of the emitting material, from microturbulence to large-scale turbulence. The strong elongation could be due to an outflow of material from the star. No radial motions of individual clusters of spots with respect to the central source in VLA 1 have been found. The presence of these spots at various epochs could be due to the passage of MHD waves, which excite the maser emission in corresponding zones of the maser source. This process could have a cyclic character, and be associated with the flare activity of the central star. 相似文献
10.
The masses of 12 protostars assumed to be the central bodies in circumstellar protoplanetary disks are estimated based on analysis of their methanol maser spectra and fine spatial structure. The calculations are based on the hypothesis that the class II methanol maser lines are formed in an edge-on Keplerian disk, while the thermal methanol emission and CS lines are formed in a cocoon around the protostar. This provides information about the velocities of the protostar and the methanol maser condensations relative to the center. In most of the star-forming regions studied, the derived masses are within limits admissible for disks around massive OB stars. The masses are in good agreement with the calculations of other authors based on models of the velocity gradients of the maser features. It is suggested that the methanol spectra display a triplet structure in which the two lateral features are class II methanol lines and the central component is a class I methanol maser line or thermal methanol line. This is consistent with the fact that the correlation of regions of maser emission with regions of emission of dense molecular gas in the CS line is about twice as strong(about 100%) as the correlation with ultracompact HII regions (about 50%). This should be taken into account when modeling protoplanetary disks and star-forming regions. 相似文献
11.
12.
O. S. Bayandina I. E. Val’tts S. E. Kurtz G. M. Rudnitskij A. V. Alakoz 《Astronomy Reports》2017,61(6):487-502
We report H2O maser line observations of the bright-rimmed globule IC 1396 N using a ground-space interferometer with the 10-m RadioAstron radio telescope as the space-based element. The source was not detected on projected baselines >2.3. Earth diameters, which indicates a lower limit on the maser size of L > 0.03 AU and an upper limit on the brightness temperature of 6.25 × 1012 K. Fringe-rate maps are prepared based on data from ground-ground baselines. Positions, velocities and flux densities of maser spots were determined. Multiple low-velocity features from ?4.5 km/s to +0.7 km/s are seen, and two high-velocity features of V LSR = ?9.4 km/s and V LSR = +4.4 km/s are found at projected distances of 157 AU and 70 AU, respectively, from the strongest low-velocity feature at V LSR = ~+0.3 km/s. Maser components from the central part of the spectrum fall into four velocity groups but into three spatial groups. Three spatial groups of low-velocity features detected in the 2014 observations are arranged in a linear structure about ~200 AU in length. Two of these groups were not detected in 1996 and possibly are jets which formed between 1996 and 2014. The putative jet seems to have changed direction in 18 years, which we explain by the precession of the jet under the influence of the gravity of material surrounding the globule. The jet collimation can be provided by a circumstellar protoplanetary disk. There is a straight line orientation in the “V LSR-Right Ascension” diagram between the jet and the maser group at V LSR = ~+0.3 km/s. However, the central group with the same position but at the velocity V LSR ~ ?3.4 km/s falls on a straight line between two high-velocity components detected in 2014. Comparison of the low-velocity positions from 2014 and 1996, based on the same V LSR-Right Ascension diagram for low-velocity features, shows that the majority of the masers maintain their positions near the central velocity V LSR = ~0.3 km/s during the 18 year period. 相似文献
13.
We report the results of monitoring the H2O maser in NGC 7538, which is associated with a star-forming region. The observations were carried out on the 22-meter telescope of the Pushchino Radio Astronomy Observatory. Two intervals of long-term variability of the integrated flux that reflect the cyclic activity of the maser have been distinguished (1981–1992 and 1993–2003); the data for the earlier activity cycle, 1981–1992, have been analyzed. The period of the long-time-scale variations is about 13–14 years. Flares of individual spectral features and of two groups of features with mean radial velocities of ?60 and ?46.6 km/s have been observed. The flares lasted from 0.3 to 1 year. The emission features observed during the 1984–1985 flare at radial velocities between ?62 and ?58 km/s probably form a spatially compact group of spots (<1015 cm) in NGC 7538 IRS 1. The triplet structure of the spectra can be traced. The observed anticorrelations and correlations of the fluxes of the triplet components suggest that the maser spots may be located either in a protoplanetary disk or in a high-velocity gaseous outflow. 相似文献
14.
Strong flares of the H2O maser emission in sources associated with active star-forming regions are analyzed. The main characteristics of 13 flares
in nine sources selected using special criteria are presented. The observed phenomena are explained as flares in double emission
features. The approach of two emission features in the spectrum with increasing flux and their recession with decreasing flux
is explained using a model with two physically related clumps of material that are partially superposed in the line of sight.
Calculations have shown that, in this type of model, exponential amplification (unsaturated maser emission) in the overlapping
parts of the clumps can produce the observed line narrowing with increasing flux. In most cases, the maser spots are inhomogeneous.
During the evolution of some flares, the maser condensations may split into separate fragments. A less catastrophic evolutionary
path may be an initial stage of formation of chainlike structures, which are fairly widespread in envelopes around ultracompact
HII regions. 相似文献
15.
The paper reports the results of observations of the H2O maser in S255 carried out in 1982–1985 and 1990–2000 on the 22-meter telescope of the Pushchino Radio Astronomy Observatory. The H2O maser emission extends from ?2 to 14 km/s and is mainly concentrated in three radial-velocity intervals. The velocity of the central group of emission features coincides with that of the molecular cloud, while the two lateral groups (blueshifted and redshifted) are positioned in the spectrum more or less symmetrically relative to the central feature. During the monitoring of S255, two phenomena were observed. First, the integrated flux of the H2O maser emission varied in a cyclic manner with a period of two to four years; this may be connected with activity of the protostar. Second, the fluxes of emission features (or groups of features) were anticorrelated. The emission of the three groups of features noted above dominated in succession. In some time intervals, a triplet spectral structure with anticorrelation between the fluxes of the lateral components and of the central and lateral components was observed. The flux anticorrelation between groups of features and individual features could be due to competition between spatial emission pumping modes in a nonuniform Keplerian disk. 相似文献
16.
V. V. Krasnov E. E. Lekht V. M. Minnebaev M. I. Pashchenko G. M. Rudnitskii A. M. Tolmachev 《Astronomy Reports》2018,62(3):200-212
The results of monitoring the H2O maser observed toward the region GH2O 092.67+03.07 (IRAS 21078+5211) located in the Giant Molecular Cloud Cygnus OB7 are presented. The observations were carried out with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 2006–2017. Strong flares of the H2O maser emission with flux densities up to 19 800 Jy were detected. The flares exhibited both global (over the source) and local characters. All the flares were accompanied by strong variations in the H2O spectra within the corresponding radial-velocity ranges. Individual H2O components form both compact clusters and chains 1–2-AU long. Analysis of the variations of the fluxes, radial velocities, and line shapes of features during the flares showed that the medium may be strongly fragmented, with small-scale turbulent motions taking place in the H2Omaser region. 相似文献
17.
Results of monitoring of H2O maser in the infrared source IRAS 20126+4104, which is associated with a cool molecular cloud, are presented. The observations were carried out on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia) between June 1991 and January 2006. The spectrum of the H2O maser emission extends from ? 16.7 to 4.8 km/s and splits into separate groups of emission features. Cyclic variations of the integrated maser flux with a period from 3.4 to 5.5 years were detected, together with strong flares of up to 220 Jy in individual emission features. It is shown that large linewidths in periods of high maser activity are due to small-scale turbulent motions of the material. An expanding envelope around a young star is accepted as a model for the source. The protostar has a small peculiar velocity with respect to the molecular cloud (～2 km/s). Individual emission features form organized structures, including multi-link chains. 相似文献
18.
Results of monitoring of the H2O maser observed toward the infrared source IRAS 21078+5211 in the giant molecular cloud Cygnus OB7 are presented. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from April 1992 to March 2006. Five cycles of maser activity at various levels were observed. In the periods of highest activity, the spectrum of the H2O maser emission extended from ?43 to 12 km/s. During strong flares, the flux densities in some emission features reached nearly 600 Jy. The protostar has a small peculiar velocity with respect to the CO molecular cloud (～2 km/s). Based on the character of the radial-velocity variations and the tendency for the linewidth to increase with the flux, it is concluded that the medium is strongly fragmented and that there is a small-scale turbulent outflow of ga in the H2O maser region, which may impede the formation of an HII region. The asymmetric distribution of the maser components in V LSR, the difference in the average linewidths of the central and lateral clusters of components, and the fairly high radial velocities relative to the molecular cloud (especially during periods of the highest maser activity) suggest that the maser spots belong to different clusters and different structures of the source: a disk and bipolar outflow. 相似文献
19.
Results of a study of a strong flare of H2O maser emission in the star-forming region Sgr B2(M) in 2004 are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. The main emission, with its flux density reaching 3800 Jy, was concentrated in a narrow radial-velocity interval (about 3 km/s) and was most likely associated with the compact group r, while the emission at VLSR > 64 km/s came from group q. After 1994, the variations of the H2O maser emission in Sgr B2(M) became cyclic with a mean period of 3 years. 相似文献
20.
G. M. Rudnitskii E. E. Lekht O. S. Bayandina I. E. Val’tts E. R. Khan 《Astronomy Reports》2016,60(1):129-144
Observations of H2O maser sources at 1.35 cm associated with extended regions of 4.5-µm emission (indicated as “green” on Spitzer survey maps—so-called Extended Green Objects, EGOs) are reported. EGOs are considered as characteristic signposts of regions of formation of massive stars, which host high-velocity outflows, as well as methanol, water, and hydroxyl masers. The observations were carried out in January–May 2015 on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory. The sample studied includes 24 EGOs north of declination -29° taken from the Spitzer GLIMPSE survey, together with one of the brightest Class I methanol masers G6.05-1.45 (M8E) and the Class I methanol maser in an IRDC G359.94+0.17. H2O maser emission was detected toward 11 of the EGOs: G11.94-0.62, G14.33-0.64, G16.59-0.06, G23.01-0.41, G24.943+0.074, G28.83-0.25, G34.3+0.2, G34.403+0.233, G35.20-0.74, G45.47+0.07, and G49.267-0.337. These including the well known H2O maser in the W44 region, G34.3+0.2. H2O emission from G28.83-0.25 was detected for the first time, at 77.6 km/s, with a flux density of 19 Jy in January and 16 Jy in February 2015. The source was probably caught at an early stage of the propagation of a shock wave. The Class I methanol masers G359.94+0.17 and G6.05-1.45 (M8E) and 13 of the EGOs were not detected in the H2O line, with 3s upper limits of ~6-7 Jy. Spectra and maser-emission parameters are given for the detected H2Omasers, for some of which strong variability of the H2O maser emission was observed. The detected H2Omasers, together with the Class I methanol masers and extended 4.5-µm emission, are associated with a very early stage in the development of young stellar objects in the regions of the EGOs. However, this sample of EGOs is not uniform. The presence of 44-GHz Class I methanol masers together with EGOs cannot be considered the only sign of early stages of star formation. 相似文献