共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
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
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.
We present the observations of the H2O maser in S140 with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 1992–1999. The H2O maser emission is mainly concentrated in three symmetrically placed narrow radial-velocity intervals. In contrast to our earlier observations (1981–1991), we did not detect emission simultaneously in all three intervals; instead, the emission appeared successively in each. We discuss possible origins for this behavior. To explain the flux variability and radial-velocity drift of the main components, we propose a model with Keplerian orbital motion of clumps (protoplanets) and calculate their orbital parameters. 相似文献
5.
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
6.
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
7.
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
8.
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
9.
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
10.
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
11.
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
12.
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
13.
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14.
P. Colom E. E. Lekht M. I. Pashchenko G. M. Rudnitskii A. M. Tolmachev 《Astronomy Reports》2016,60(8):730-743
The results of a study of the H2O and OH maser emission from the cool IR source IRAS 16293?2422 are presented. The observations analyzed were obtained in H2O lines with the 22-m telescope of the Pushchino Radio Astronomy Observatory during 1999–2015 and in OH lines with the Nanc¸ ay radio telescope (France). A large number of very strong flares of the H2O maser were detected, reaching fluxes of tens of thousands of Jansky. Individual features can form organized structures resembling chains ～2 AU in length with a radial-velocity gradient along them. The observed drift of the H2O emission (2003–2004) in space and velocity (from 4.3 to 5.3 km/s) is not due solely to proper motion of the features. The other origin of the drift is a drift of the emission maximum during a flare as the shock consecutively excites spatially separated features in the structure in the form of a chain. The OH-line observations at 18 cm show that the emission remains unpolarized and thermal, with a line width of 0.7 km/s, which corresponds to a cloud temperature of ～30 K. 相似文献
15.
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
16.
P. Colom E. E. Lekht M. I. Pashchenko G. M. Rudnitskii A. M. Tolmachev 《Astronomy Reports》2017,61(12):1061-1072
The results of a study of the maser source G 10.623-0.383 in the λ = 1.35 cm H2O line using the 22-mradio telescope of the Pushchino Radio AstronomyObservatory (Russia) and in the main hydroxyl lines (λ = 18 cm) using the Nanзay Radio Telescope (France) are presented. Uncorrelated long-term variations of the integrated intensities and the velocity centroids with characteristic times of 11 yrs (mean value) and 32 yrs, respectively, are studied. The drift of the velocity centroid may be associated with maser condensations whose material is collapsing onto the OB cluster. It is shown that the H2O maser source contains maser condensation configurations on various scales over a long time, which evolve with time. OH maser emission was only detected in the main lines at 1665 and 1667 MHz. The flux densities of the strongest emission components were variable, but their radial velocities did not change. A Zeeman pair was found at 1667 MHz with a splitting of about 1.44 km/s, corresponding to a line-of-sight magnetic field of 4.1 mG, which was preserved over at least 25 years. The characteristics of the H2O andOHmaser variability suggests that the masers are located in different parts of G 10.623–0.383. 相似文献
17.
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
18.
The results of observations of the H2O and OH maser sources toward the region of W33C (G12.8-0.2) are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in the 1.35-cm water-vapor line and on the Large Radio Telescope at Nan?ay (France), in the main (1665 and 1667 MHz) and satellite (1612 and 1720 MHz) OH lines. Multiple, strongly variable, short-lived H2O emission features were detected in a broad interval of radial velocities, from ?7 to 55 km/s. OH maser emission in the 1667-MHz line was detected at velocities of 35?C41 km/s. The Stokes parameters of the maser emission in the main OH lines 1665 and 1667 MHz were measured. Zeeman splitting was detected in the 1665-MHz line at 33.4 and 39.4 km/s, and in the 1667 MHz line only at 39.4 km/s. The magnetic-field intensity was estimated. Appreciable variability of the Zeeman splitting components was observed at 39 and 39.8 km/s in both main lines. The extended spectrum and fast variability of the H2O maser emission, together with the variability of the Zeeman-splitting components in the main OH lines, may indicate a composite clumpy structure of the molecular cloud and the presence of large-scale rotation, bipolar outflows, and turbulent motions of material in this cloud. 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.
We report the results of a study of fast variations of the H2O maser emission toward NGC 7538 IRS 1, which is associated with a star-forming region. The study is based on monitoring data
in the 1.35 cm line obtained in 1996–2003 on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia).
Periodic flux variations of four long-lived emission features with an average period of about 0.9 year have been detected.
The flux variations of these features are correlated, suggesting that the detected variability is a consequence of pulsation
of, e.g., stellar wind from the protostar in NGC 7538 IRS 1, with a period of about 0.9 year (0.87 ± 0.03 year). These pulsations
are superimposed on long-term variability of the integrated maser emission with a period of 13 years. 相似文献