Proper Motions and Distances of Water Maser Complexes

1984 ◽  
pp. 335-338
Author(s):  
M. H. Schneps ◽  
M. J. Reid ◽  
J. M. Moran ◽  
R. Genzel ◽  
D. Downes ◽  
...  
Keyword(s):  
Proper Motions ◽  
Water Maser

scholarly journals Masers as probes of proto-planetary discs

2004 ◽  
Vol 202 ◽  
pp. 362-364
Author(s):  
A.M.S. Richards ◽  
R. J. Cohen ◽  
M. Crocker ◽  
E. E. Lekht ◽  
V. Samodourov ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Radio Telescope ◽  
Keplerian Orbit ◽  
Proper Motions ◽  
Central Mass ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
Velocity Variations ◽  
Water Maser

Water maser emission from star forming regions has been monitored for several decades using the Puschino radio telescope, showing radial velocity variations consistent with material in Keplerian orbit around protostars. MERLIN and the EVN are now being used to image the 22 GHz emission on au scales and measure proper motions. This will distinguish discs from outflows, and provide an estimate of the central mass and possibly orbiting condensations.

scholarly journals Proper Motions and Distances of Water Maser Complexes

1984 ◽  
Vol 110 ◽  
pp. 335-338
Author(s):  
M. H. Schneps ◽  
M. J. Reid ◽  
J. M. Moran ◽  
R. Genzel ◽  
D. Downes ◽  
...  
Keyword(s):  
Spectral Line ◽  
Galactic Center ◽  
Three Dimensional ◽  
Proper Motions ◽  
Preliminary Results ◽  
First Results ◽  
Maser Sources ◽  
Water Maser

We report preliminary results of a long term spectral line VLBI experiment to observe internal proper motions of water maser sources in the vicinity of newly formed stars. This technique yields a picture of the three-dimensional kinematics of the region and a measure of the distance to the source. First results from the galactic center source SGR B2 are presented.

scholarly journals A collimated molecular jet in W 43A traced by water maser emission

2002 ◽  
Vol 206 ◽  
pp. 80-83
Author(s):  
Hiroshi Imai ◽  
Tetsuo Sasao ◽  
Kumiko Obara ◽  
Toshihiro Omodaka ◽  
Philip J. Diamond
Keyword(s):  
Stellar Evolution ◽  
Position Angle ◽  
Proper Motions ◽  
Maser Emission ◽  
Water Masers ◽  
Water Maser

We present the spatial and velocity distributions of water masers in W 43A. Most of the maser features are spatially and kinematically collimated to a surprising extent. It is very likely that the jet in W 43A is predominantly composed of warm molecules traced by water maser emission. The position angle of the spatial collimation of the maser clusters is slightly different from the directions of both the cluster separation and the proper motions. We propose a model involving a precessing jet to explain the axis offsets. The discovery of a molecular jet with precession in W 43A provides important information on our understanding of the formation of collimated molecular jets and may provide clues on specific stages of stellar evolution.

scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2020 ◽  
Vol 635 ◽  
pp. A118
Author(s):  
L. Moscadelli ◽  
A. Sanna ◽  
C. Goddi ◽  
V. Krishnan ◽  
F. Massi ◽  
...  
Keyword(s):  
Thermal Emission ◽  
Three Dimensional ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
High Mass ◽  
Proper Motions ◽  
Long Baseline ◽  
Protostellar Outflows ◽  
Water Masers ◽  
Water Maser

Context. 22 GHz water masers are the most intense and widespread masers in star-forming regions. They are commonly associated with protostellar winds and jets emerging from low- and high-mass young stellar objects (YSO). Aims. We wish to perform for the first time a statistical study of the location and motion of individual water maser cloudlets, characterized by typical sizes that are within a few au, with respect to the weak radio thermal emission from YSOs. Methods. For this purpose, we have been carrying out the Protostellar Outflows at the EarliesT Stages survey of a sample (38) of high-mass YSOs. The 22 GHz water maser positions and three-dimensional (3D) velocities were determined through multi-epoch Very Long Baseline Array observations with accuracies of a few milliarcsec (mas) and a few km s−1, respectively. The position of the ionized core of the protostellar wind, marking the YSO, was determined through sensitive radio continuum, multi-frequency Jansky Very Large Array observations with a typical error of ≈20 mas. Results. The statistic of the separation of the water masers from the radio continuum shows that 84% of the masers are found within 1000 au from the YSO and 45% of them are within 200 au. Therefore, we can conclude that the 22 GHz water masers are a reliable proxy for locating the position of the YSO. The distribution of maser luminosity is strongly peaked towards low values, indicating that about half of the maser population is still undetected with the current Very Long Baseline Interferometry detection thresholds of 50–100 mJy beam−1. Next-generation, sensitive (at the nJy level) radio interferometers will have the capability to exploit these weak masers for an improved sampling of the velocity and magnetic fields around the YSOs. The average direction of the water maser proper motions provides a statistically-significant estimate for the orientation of the jet emitted by the YSO: 55% of the maser proper motions are directed on the sky within an angle of 30° from the jet axis. Finally, we show that our measurements of 3D maser velocities statistically support models in which water maser emission arises from planar shocks with propagation direction close to the plane of the sky.

scholarly journals VERA observation of the massive star forming region G34.4+0.23

2007 ◽  
Vol 3 (S248) ◽  
pp. 202-203
Author(s):  
T. Kurayama
Keyword(s):  
Massive Star ◽  
Proper Motions ◽  
Star Forming ◽  
Dark Clouds ◽  
Structure Phase ◽  
Infrared Dark Clouds ◽  
Water Maser

AbstractWe observed with VERA the massive star forming region G34.4+0.23, to obtain parallaxes and proper motions. Four infrared dark clouds were observed and water maser were found in two dark clouds, MM1 and MM4. In MM1, the distribution of maser spots shows a “V-shaped” structure and most features co-moving with this structure. Phase-referenced images have peaks and their motion is much larger than the expected parallax. Further analysis is needed to correctly interpret our measurement of parallax.

scholarly journals A MERLIN movie of mass-loss from RT Vir

1999 ◽  
Vol 191 ◽  
pp. 315-320
Author(s):  
A. M. S. Richards ◽  
R. J. Cohen ◽  
I. Bains ◽  
J. A. Yates
Keyword(s):  
Velocity Field ◽  
Mass Loss ◽  
Angular Resolution ◽  
Simple Function ◽  
Proper Motions ◽  
Maser Emission ◽  
Stellar Velocity ◽  
The Individual ◽  
Water Maser

We used MERLIN to observe RT Vir at 22 GHz at six epochs during 10 weeks. The water maser emission comes from a thick expanding shell with an elliptical velocity field. MERLIN has a velocity resolution of 0.1 km s−1 and milli-arcsecond angular resolution, revealing details within the individual maser clouds, typically 12 mas in diameter spanning 15 velocity channels. The brightest peak doubles in intensity to 800 Jy/beam. Features at velocities close to the stellar velocity show the largest proper motions of ∼ 3 mas away from the centre of emission. Some features are seen near the outer limits to the maser shell at early epochs only, but new masers appear close to the inner rim. The variability of individual maser features is not a simple function of the stellar luminosity.

scholarly journals Astrometric observations of water maser sources toward the Galactic Center with VLBI

2021 ◽  
Vol 2145 (1) ◽  
pp. 012011
Author(s):  
D Sakai ◽  
T Oyama ◽  
T Nagayama ◽  
H Kobayashi ◽  
M Honma
Keyword(s):  
Molecular Clouds ◽  
Galactic Center ◽  
Galactic Disk ◽  
Kinematic Model ◽  
Three Dimensional ◽  
Circular Motion ◽  
Proper Motions ◽  
Center Region ◽  
Maser Sources ◽  
Water Maser

Abstract The Central Molecular Zone (CMZ) in the Galactic Center region shows outstanding non-circular motion unlike the Galactic disk. Although several models describing this non-circular motion are proposed, an uniform kinematic model of the CMZ orbit is not appeared. Three dimensional velocity information including proper motions will be critical to constrain the orbital models of the CMZ because most of models proposed are devised to reproduce the line-of-sight velocity pro les of the molecular clouds in this region. To reveal the dynamics of the Galactic center region, we conducted VLBI astrometric observations of 22 GHz water maser sources toward the Galactic center with VERA. By measuring parallaxes and proper motions, we can identify whether each source is actually located in the CMZ or not, and identify the three dimensional positions and velocities in the non-circular orbit if the source is located in the CMZ. We show the results of astrometric study for several maser sources associated with molecular clouds toward the Galactic center including Sgr B2 complex and Sgr D HII region. The parallax measurement toward Sgr B2 obtained the parallax of 0.133 0:038 mas, and its proper motions indicated that Sgr B2 complex is moving toward the positive Galactic longitude with V = 100 km s−1 relative to Sgr A*.

scholarly journals VLBA multi-epoch water maser observations towards Cepheus A

2002 ◽  
Vol 206 ◽  
pp. 84-87
Author(s):  
José M. Torrelles ◽  
Nimesh A. Patel ◽  
José F. Gómez ◽  
Paul T. P. Ho ◽  
Luiz F. Rodríguez ◽  
...  
Keyword(s):  
Star Formation ◽  
Theoretical Studies ◽  
Proper Motions ◽  
Star Formation Activity ◽  
Remarkable Result ◽  
Water Masers ◽  
Cepheus A ◽  
Water Maser

We have carried out and recently reported VLBA multi-epoch water maser observations toward Cepheus A with an angular and velocity resolution of 0.5 mas and 0.2 km s−1, respectively. Some of the masers detected previously with the VLA (observations made with angular and velocity resolutions of 80 mas and 1.3 km s−1, respectively) are resolved now into linear/arcuate coherent “microstructures”. These structures, while smaller than the VLA beam, are 6-200 times the size of the VLBA synthesized beam. The morphology and the observed proper motions found in these structures imply three different centers of star formation activity in a region of ⋍ 0.3 radius (⋍ 200 AU). The most remarkable result from these observations is the discovery of an arc of water masers which is perfectly fitted by a circle to one part in a thousand. This arc is expanding and suggests a spherical “puff” of ejected material ejected 33 years ago from a protostar located 600 mas south of the radio jet HW2. This spherical ejection represents a very strong challenge for theoretical studies of star formation.

scholarly journals The H2O maser proper motions of RT Vir and VX Sgr

2002 ◽  
Vol 206 ◽  
pp. 298-305
Author(s):  
Jeremy Yates ◽  
Anita Richards ◽  
Malcolm Gray
Keyword(s):  
Magnetic Field ◽  
Mass Loss ◽  
Proper Motion ◽  
Numerical Models ◽  
Small Radius ◽  
Circumstellar Envelope ◽  
Proper Motions ◽  
Radial Acceleration ◽  
Magnetic Field Axis ◽  
Water Maser

We have measured significant proper motions using the water maser clouds in the outflows from RT Vir (6 epochs) and VX Sgr (2 epochs). In both cases proper motions are measured in the bright emission found perpendicular to the OH emission. This strongly suggests latitude dependent mass-loss with the water masers tracing a dense equatorial outflow and the OH emission tracing a less dense polar outflow. In both cases the rotational velocities are < 1 km s−1 thus ruling out a strongly rotating circumstellar envelope. This suggests the outflow is not shaped by an orbiting companion. In the case of VX Sgr the proper motions are contained in a wedge perpendicular to the measured magnetic field axis, thus strongly suggesting that the magnetic field is helping to shape the mass outflow.The proper motion results have thrown up a puzzle. For VX Sgr the material is being radially accelerated and material enters the water maser zone at 4 km s−1. This is consistent with the mass loss model of Bowen (1988). However the RT Vir proper motion results show no such radial acceleration. The masers have already received their acceleration before they reach the water maser zone at 3-AU (our numerical models seem to support the small radius). This was probably done in the pulsation zone. The acceleration mechanism is unclear for this source.

Proper Motions of Water Masers in Circumstellar Shells

1998 ◽  
Vol 164 ◽  
pp. 253-254
Author(s):  
K. B. Marvel ◽  
P. J. Diamond ◽  
A. J. Kemball
Keyword(s):  
Circumstellar Envelope ◽  
Proper Motions ◽  
Complex Region ◽  
Circumstellar Shells ◽  
Water Masers ◽  
Water Maser

AbstractWe present measurements of proper motions for circumstellar water maser observations obtained with the VLBA. Results of the observations and modeling indicate that the water masers exist in a kinematically complex region of the circumstellar envelope. A change in position of the maser spots as a function of velocity is discussed.

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