首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
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   

2.
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   

3.
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   

4.
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   

5.
An analysis of the H2O maser emission associated with protoplanetary disks is presented. Triplet H2O spectra can be formed at certain stages in the evolution of Keplerian disks. The dependence of the mass of the central star in the Keplerian disk on the disk radius is derived. The calculations are based on the distribution of the water-vapor molecules (maser spots). In S140, the observed elongated maser spots (chains) with a smoothly varying line-of-sight velocity are interpreted as protoplanetary structures with a small intrinsic rotation.  相似文献   

6.
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   

7.
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   

8.
A probable model for the circumstellar envelope associated with the source VLA 2 in W75N has been constructed, based on H2O-maser monitoring toward W75N carried out on the 22-m radio telescope in Pushchino, as well as VLA maps for 1992, 1996, 1998, and 1999. The envelope has a complex hierarchical structure, including individual maser spots, clusters and chains of spots, inhomogeneous filaments, individual arc-shaped layers, and other complicated features. Most widespread are multi-link chains or filaments with sizes of 1–2 AU. This pattern arises due to the complex hierarchical structure of turbulent motions of material on various scales, from microturbulence to large-scale chaotic motions. No expansion of individual layers in the envelope of VLA 2 has been found. The appearance of the layers is due to the passage of MHD waves that excite the maser emission in consecutive shells in the envelope. This process is fairly cyclic, and is related to the flare activity of the star.  相似文献   

9.
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   

10.
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   

11.
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   

12.
The water-vapor maser emission in the source G10.6-0.4 associated with an active starforming region (OB star cluster) is analyzed. The maser was monitored from 1981–2004 using the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory. Statistical processing of the results revealed the presence of structural formations on various scales. The individual H2O maser features may form ordered structures with velocity (V LSR) gradients, localized in separate clusters of maser features. The statistical variations of the V LSR values for the maser components may be due to the accretion of material onto the OB star cluster in G10.6-0.4 together with the rotation of the molecular cloud core. A model with a rotating, nonuniform condensation of accreted material in the vicinity of the stellar cluster is proposed to explain the variations of the velocity centroid of the H2O spectra. The integrated flux variations are explained well by a model in which the central source is an OB star cluster, possibly containing five to six stars. An important role in the evolution of the maser emission, as well as of the source as a whole, may be played by turbulent motions of the gas.  相似文献   

13.
Results of monitoring hydroxyl and water masers in the star-forming region S128 are presented. A large number of emission features in the 1665 MHz OH line have been detected in both circular polarizations. In spite of the strong variability of the flux density in the main 1665 MHz line, the radial velocities of the features remained constant. Zeeman splitting of the 1720MHz line equal to 0.86 km/s was detected, corresponding to a longitudinal magnetic field of 3.6 mG. The variability of the H2O emission has a cyclic character with a quasi-period of 4–14 yrs. The evolution of individual features confirms that the H2O sources A and B are associated with an ionization front between two colliding CO clouds, and shows that the activity was transferred from maser B to maser A in 1999–2001.  相似文献   

14.
Results of monitoring the H2O and OH masers in W44C, located near the cometary HII region G34.3+0.15, are reported. Observations in the water-vapor line at λ = 1.35 cm were carried out on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from November 1979 to March 2011, and in the hydroxyl lines at λ = 18 cm on the large Nançay radio telescope (France). Activity maxima and minima of the water maser alternated. The average period of the activity is ～ 14 years, consistent with results obtained earlier for a number of other sources associated with regions of active star formation. In periods of enhanced maser activity, two series of strong H2O maser flares were observed, which were related to two different clusters of maser spots located at the front of a shock at the periphery of the ultracompact region UH II. These series of flares may be associated with cyclic activity of the protostellar object in UH II. In the remaining time intervals, there were mainly short-lived flares of single features. The Stokes parameters for the observations in the hydroxyl lines were determined. Zeeman splitting was observed in the profile of the 1667 MHz OH main line at a velocity of 58.5 km/s, and was used to estimate the intensity of the line-of-sight component of the magnetic field (1.2 mG).  相似文献   

15.
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   

16.
The results of observations of OH (λ = 18 cm) and H2O (λ = 1.35 cm) masers toward AS 501 obtained with the Nançay Observatory Radio Telescope (France) and the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia), respectively, are presented. Nine cycles of H2O maser activity ranging from 2.8 to 6.0 years were detected, identifying AS 501 as an irregular variable star. Zeeman splitting was found only in the 1612-MHz satellite line at ?59.2 km/s. The splitting is 0.11 km/s, corresponding to a line-of-sight magnetic field strength of 0.48 mG. The field is directed toward the observer. The detected radial-velocity drift of the H2O emission features can be explained in a model with elongated filaments with radial-velocity gradients.  相似文献   

17.
The results of observations of the S128 H2O maser carried out from February 1995 to March 2001 on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory are presented. Two activity cycles of the H2O maser with a period of about 10 years were observed during the total monitoring interval (1981–2001). This may be connected either with cyclic activity of the central star in S128 during its formation or with the influence on the H2O masering region of shocks arising near an ionization front at the interface of two colliding CO clouds. The emission at radial velocities from ?73 to ?70 km/s consists of four emission features. The emission feature at ?71.8 km/s exhibits a flux dependence on linewidth that is typical of an unsaturated maser.  相似文献   

18.
Results of observations of the H2O maser in S269 carried out from October 1980 to February 2001 on the 22-m telescope (RT-22) of the Pushchino Radio Astronomy Observatory are presented. During the monitoring of S269, variability of the integrated flux of the maser emission with a cyclic character and an average period of 5.7 years was observed. This may be connected with cyclic activity of the central star during its formation. Emission at radial velocities of 4–7 km/s was detected. Thus, the H2O maser emission in S269 extends from 4 to 22 km/s, and is concentrated in three radial-velocity intervals: 4–7, 11–14, and 14–22 km/s. In some time intervals, the main group of emission features (14–22 km/s) had a triplet structure. The central velocity of the total spectrum is close to the velocity of the CO molecular cloud and HII region, differing from it by an amount that is within the probable dispersion of the turbulent gas velocities in the core of the CO molecular cloud. A radial-velocity drift of the component at V LSR≈20 km/s with a period of ≈26 years has been detected. This drift is likely due to turbulent (vortical) motions of material.  相似文献   

19.
We present the results of monitoring the H2O masers in the IR sources IRAS 18265-1517 and IRAS 18277-1516 associated with the cool molecular cloud L 379, which contains high-velocity bipolar molecular jets. The sources were observed in the 1.35 cm H2O line using the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) during 1991–2004. We detected H2O maser emission from IRAS 18265-1517 at radial velocities of 17.8 and 18.4 km/s, virtually coincident with the velocity of the molecular cloud derived from CO-line observations (18.4 km/s). The maser emission towards the other source, IRAS 18277-1516, was at higher velocities than the central velocity of the CO molecular cloud. The H2O maser spots are most likely associated with a redshifted region of CO emission. Cyclic variability of the integrated H2O maser emission that may be related to cyclic activity of the central star was detected for IRAS 18277-1516. The strongest and most long-lived component (VLSR ≈ 20.6 km/s) displays a radial-velocity drift, which could be due to deceleration of a dense clump of matter (maser condensation) in the circumstellar medium during the descending branch of a strong flare. We found numerous emission features for both IRAS 18265-1517 and IRAS 18277-1516, providing evidence for fragmentation of the medium surrounding their central objects.  相似文献   

20.
Ashimbaeva  N. T.  Colom  P.  Lekht  E. E.  Pashchenko  M. I.  Rudnitskii  G. M.  Tolmachev  A. M. 《Astronomy Reports》2019,63(12):1022-1034

Results of observations of the star-forming region S252A in the 1.35-cm H2O and 18-cm OH lines obtained using the 22-m Pushchino (Russia) and Nancay (France) radio telescopes are presented. A catalog of H2O maser spectra for 1995-2019 is presented. The variability of the integrated flux has two components: a cyclic component with a time interval between cycles ~30-35 yrs and a short-period component with a mean period of about 2.6 yrs. This may reflect non-stationary formation of a protostar. It is shown that the medium where the H2O maser emission and thermal OH emission are generated is strongly fragmented, and contains small-scale turbulent motions comparable to the thermal motions of the matter. The observed drift and jumps in the radial velocity of the H2O emission features could be a consequence of complex, non-uniform structure of the maser condensations.

  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号