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 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 Probing Accretion Disks in AGN with Water Masers

1997 ◽  
Vol 163 ◽  
pp. 113-125
Author(s):  
Philip R. Maloney
Keyword(s):  
Accretion Disk ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
Quantitative Information ◽  
X Rays ◽  
Maser Emission ◽  
Radiative Efficiency ◽  
Physical Conditions ◽  
Water Masers ◽  
Water Maser

AbstractExtremely luminous extragalactic water masers – the so-called “megamasers”, with isotropic luminosities of tens to hundreds of solar luminosities – appear to be uniquely associated with active galactic nuclei. The recent survey of Braatz et al. indicates that 20% of Seyfert 2 galaxies have detectable water maser emission. Although originally suggested to arise in shocks, it now seems likely that the masers arise from the irradiation of high-pressure molecular gas by X-rays from the AGN. Quantitative modelling shows that the observed megamaser luminosities can plausibly be produced in this fashion. Both observational limits on the size scales and the high gas pressures required indicate that the water maser emission arises on very small scales, either in a circumnuclear “torus” or the accretion disk itself. In the best-studied case, NCG 4258, the masers are produced in a geometrically thin, warped accretion disk. The maser models can be used to derive quantitative information about the physical conditions in the disk, namely, the mass accretion rate, and therefore the radiative efficiency. I discuss the implications of water maser observations and models for the study of accretion disks and circumnuclear tori in AGN.

scholarly journals Monitoring of extragalactic water masers with the MPIfR 100-m telescope

2002 ◽  
Vol 206 ◽  
pp. 392-395
Author(s):  
Yoshiaki Hagiwara ◽  
Christian Henkel ◽  
William A. Sherwood
Keyword(s):  
Radio Telescope ◽  
Radio Galaxy ◽  
Maser Emission ◽  
Monitoring Period ◽  
Water Masers ◽  
Water Maser

We present single-dish monitoring of the 22 GHz water maser lines from the Seyfert 2 galaxies NGC 3079, M51(NGC 5194), NGC 5793, and the radio galaxy NGC 315 with the Effelsberg 100-m radio telescope. During the monitoring period of 1995 − 2001, the H2O masers flared in M51 and NGC 5793, while maser emission from NGC 315 was not detected in 1996 and 2000. During 2000, we discovered new red-shifted velocity features in NGC 3079 and blue-shifted features in M51. These velocity components are crucial to model the distribution of maser emission in each galaxy.

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 Powerful Water Masers in Active Galactic Nuclei

2002 ◽  
Vol 19 (4) ◽  
pp. 401-421 ◽  
Author(s):  
Philip R. Maloney
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Rotating Disk ◽  
Future Prospects ◽  
Maser Emission ◽  
X Ray ◽  
Central Engine ◽  
Water Masers ◽  
Water Maser

AbstractLuminous water maser emission in the 616–523 line at 22GHz has been detected from two dozen galaxies. In all cases the emission is confined to the nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and LINERs. I argue that most of the observed megamaser sources are powered by X-ray irradiation of dense gas by the central engine. After briefly reviewing the physics of these X-Ray Dissociation Regions, I discuss in detail the observations of the maser disk in NGC 4258, its implications, and compare alternative models for the maser emission. I then discuss the observations of the other sources that have been imaged with VLBI to date, and how they do or do not fit into the framework of a thin, rotating disk, as in NGC 4258. Finally, I briefly discuss future prospects, especially the possibility of detecting other water maser transitions.

The extraordinary outburst in NGC6334I-MM1: dimming of the hypercompact HII region and destruction of water masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 255-258
Author(s):  
Crystal L. Brogan ◽  
Todd R. Hunter ◽  
Gordon MacLeod ◽  
James O. Chibueze ◽  
Claudia J. Cyganowski
Keyword(s):  
Radio Source ◽  
Photon Production ◽  
Maser Emission ◽  
Hii Region ◽  
Thermal Radio ◽  
Water Masers ◽  
Continuum Data ◽  
Water Maser ◽  
The Continuum

AbstractWe present subarcsecond resolution pre- and post-outburst JVLA continuum and water maser observations of the massive protostellar outburst source NGC6334I-MM1. The continuum data at 5 and 1.4 cm reveal that the free-free emission powered by MM1B, modeled as a hypercompact HII region from our 2011 JVLA data, has dropped by a factor of 5.4. Additionally, the water maser emission toward MM1, which had previously been strong (500 Jy) has dramatically reduced. In contrast, the water masers in other locations in the protocluster have flared, with the strongest spots associated with CM2, a non-thermal radio source that appears to mark a shock in a jet emanating 2″ (2600 au) northward from MM1. The observed quenching of the HCHII region suggests a reduction in uv photon production due to bloating of the protostar in response to the episodic accretion event.

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 Water and OH Maser Emission from the Planetary Nebula K3-35

2003 ◽  
Vol 209 ◽  
pp. 263-266 ◽  
Author(s):  
Yolanda Gómez ◽  
Luis F. Miranda ◽  
Guillem Anglada ◽  
JosÉ M. Torrelles
Keyword(s):  
Planetary Nebula ◽  
Central Star ◽  
Minor Axis ◽  
Water Molecules ◽  
Giant Star ◽  
Maser Emission ◽  
Giant Stars ◽  
Water Masers ◽  
Unambiguous Detection ◽  
Water Maser

Water-vapour masers, typical of the envelopes in giant stars, are not expected to persist in planetary nebulae due to the ultraviolet radiation of the remnant star that progressively destroys the molecules. Recently, we have reported the first unambiguous detection of water maser emission in a planetary nebula, K 3–35 (Miranda et al. 2001). The water masers in K3–35 were detected at the center of the nebula, along the minor axis, at a radius of ~85 AU and also at the surprisingly large distance of 5000 AU from the star, at the tips of the bipolar lobes. The existence of these water molecules is puzzling, and probably we are observing the very moment of transformation of a giant star into a planetary nebula. Miranda et al. (2001) also report the presence of polarization in the OH 1665 MHz masers, which are distributed towards the central star in a torus-like structure. Here we review the main results on this source.

scholarly journals Resolving the distance controversy for Sharpless 269

2019 ◽  
Vol 625 ◽  
pp. A70 ◽  
Author(s):  
L. H. Quiroga-Nuñez ◽  
K. Immer ◽  
H. J. van Langevelde ◽  
M. J. Reid ◽  
R. A. Burns
Keyword(s):  
Proper Motion ◽  
Rotation Curve ◽  
Galactic Rotation ◽  
Distance Estimate ◽  
Large Radius ◽  
Maser Emission ◽  
Long Baseline ◽  
Galactic Rotation Curve ◽  
Water Masers ◽  
Water Maser

Context. Sharpless 269 (S 269) is one of a few HII regions in the outer spiral arm of the Milky Way with strong water maser emission. Based on data from the Very Long Baseline Interferometry (VLBI) Exploration of Radio Astrometry (VERA) array, two parallax measurements have been published, which differ by nearly 2σ. Each distance estimate supports a different structure for the outer arm. Moreover, given its large Galactocentric radii, S 269 has special relevance as its proper motion and parallax have been used to constrain the Galactic rotation curve at large radii. Aims. Using recent Very Long Baseline Array (VLBA) observations, we accurately measure the parallax and proper motion of the water masers in S 269. We interpret the position and motion of S 269 in the context of Galactic structure, and possible optical counterparts. Methods. S 269’s 22 GHz water masers and two close by quasars were observed at 16 epochs between 2015 and 2016 using the VLBA. We calibrated the data by inverse phase referencing using the strongest maser spot. The parallax and proper motion were fitted using the standard protocols of the Bar and Spiral Structure Legacy survey. Results. We measure an annual parallax for S 269 of 0.241 ± 0.012 mas corresponding to a distance from the Sun of 4.15+0.22−0.20 kpc by fitting four maser spots. The mean proper motion for S 269 was estimated as 0.16 ± 0.26 mas yr−1 and −0.51 ± 0.26 mas yr−1 for μα cosδ and μδ respectively, which corresponds to the motion expected for a flat Galactic rotation curve at large radius. This distance estimate, Galactic kinematic simulations and observations of other massive young stars in the outer region support the existence of a kink in the outer arm at l ≈ 140°. Additionally, we find more than 2000 optical sources in the Gaia DR2 catalog within 125 pc radius around the 3D position of the water maser emission; from those only three sources are likely members of the same stellar association that contains the young massive star responsible for the maser emission (S 269 IRS 2w).

scholarly journals First detection of vibrationally excited water masers toward embedded young stellar objects

2002 ◽  
Vol 206 ◽  
pp. 55-58
Author(s):  
Tarja Liljeström ◽  
Anders Winnberg ◽  
Roy Booth
Keyword(s):  
Young Stellar Objects ◽  
Circumstellar Envelope ◽  
Vibrationally Excited ◽  
Stellar Objects ◽  
Maser Emission ◽  
Hot Gas ◽  
Water Masers ◽  
Water Maser

We report the first detection of vibrationally excited water maser emission in the circumstellar envelope of two young stellar objects (W51M, Z CMa). The results suggest that the observed 96 GHz water maser emission traces hot gas in an accretional stage of the protostellar evolution.

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