Very long baseline interferometric observations of the H20 sources inW49N, W3(OH), ORI A, and VY CMa.

Moran, J. M.; Papadopoulos, George; Burke, B. F.; Lo, K. Y.; Schwartz, P. R.; Thacker, D. L.

doi:10.1086/152437

Cited by 39 publications

(21 citation statements)

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“…Scattering effects can often play a role in the broadening of the maser images as argued by Moran et al (1973) for OH and H 2 O masers in W49N. They found that "the ratio of the size of the smallest OH masers to that of the smallest H 2 O masers was nearly equal the ratio of the squares of the wavelengths".…”

Section: Scattering Effectsmentioning

confidence: 93%

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

Minier

Booth

Conway

2002

A&A

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Abstract. We consider the milliarsecond scale structures of three representative methanol maser sites observed at high resolution with the EVN at 6.7 GHz and with the VLBA at 12.2 GHz. These observations suggest that the majority of the individual masing regions within a maser site consist of a compact core surrounded by extended emission, i.e. a core/halo structure. In many cases, the extended emission is resolved by the shortest baselines of the VLBA. We conclude that these regions of extended emission are responsible for the missing flux density when comparing cross-power spectra on the shortest VLBI baselines to single dish spectra. The halos of diffuse emission have diameters ranging between 12 and 290 AU and their brightness temperatures depend on their diameters as T b ∝d −2.2 . The core diameters vary from 2 to 20 AU. Three possible phenomena could explain the presence of large halos around bright cores. The core/halo pattern could be the result of saturation effects in a uniform spherical maser cloud. The compact and diffuse masers could also originate in physically distinct regions: the maser core could form within highly dense gas while the maser halo could be the result of weak masers in diffuse gas. Finally, turbulence could cause the appearance of core/halo structures in a disrupted homogeneous medium. Scattering effects do not seem to play a role in the broadening of maser images since masers have similar sizes at 6.7 and 12.2 GHz.

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Section: Scattering Effectsmentioning

confidence: 93%

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

Minier

Booth

Conway

2002

A&A

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“…Four interferometric studies provide information about the spatial distribution of the 22 GHz water maser emission in W49N over a 30 yr time period (Moran et al 1973;Walker et al 1982;Gwinn et al 1992;McGrath et al 2004;performed in 1970-71, 1978-82, and 1998. They indicate that 99% of the 22 GHz maser flux is associated with the ultracompact H ii regions designated G1 and G2 (Dreher et al 1984), and originates within 5 of the beam center position adopted for our Herschel (and Effelsberg) observations.…”

Section: Pointed Observations Toward W49n and Orion Southmentioning

confidence: 99%

HERSCHEL/HIFI OBSERVATIONS OF A NEW INTERSTELLAR WATER MASER: THE 5₃₂-4₄₁TRANSITION AT 620.701 GHz

Neufeld

Kraus

et al. 2013

ApJ

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Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have performed mapping observations of the 620.701 GHz 5 32 -4 41 transition of ortho-H 2 O within a ∼1. 5 × 1. 5 region encompassing the Kleinmann-Low nebula in Orion (Orion-KL), and pointed observations of that transition toward the Orion South condensation and the W49N region of high-mass star formation. Using the Effelsberg 100 m radio telescope, we obtained ancillary observations of the 22.23508 GHz 6 16 -5 23 water maser transition; in the case of Orion-KL, the 621 GHz and 22 GHz observations were carried out within 10 days of each other. The 621 GHz water line emission shows clear evidence for strong maser amplification in all three sources, exhibiting narrow (∼1 km s −1 FWHM) emission features that are coincident (kinematically and/or spatially) with observed 22 GHz features. Moreover, in the case of W49N-for which observations were available at three epochs spanning a 2 yr period-the spectra exhibited variability. The observed 621 GHz/22 GHz line ratios are consistent with a maser pumping model in which the population inversions arise from the combined effects of collisional excitation and spontaneous radiative decay, and the inferred physical conditions can plausibly arise in gas heated by either dissociative or non-dissociative shocks. The collisional excitation model also predicts that the 22 GHz population inversion will be quenched at higher densities than that of the 621 GHz transition, providing a natural explanation for the observational fact that 22 GHz maser emission appears to be a necessary but insufficient condition for 621 GHz maser emission.

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“…A blank entry in the SiO column indicates the source was not observed. See Sevenster (2002aSevenster ( , 2002b strongest hyperfine components of this transition (Moran et al 1973). No other hyperfine splitting effects are taken into account.…”

Section: Sample Selectionmentioning

confidence: 99%

H₂O Maser Observations of Candidate Post‐AGB Stars and Discovery of Three High‐Velocity Water Sources

Deacon

Chapman

Green

et al. 2007

ApJ

106

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We present the results of 22 GHz H 2 O maser observations of a sample of 85 postYasymptotic giant branch ( post-AGB) candidate stars, selected on the basis of their OH 1612 MHz maser and far-infrared properties. All sources were observed with the Tidbinbilla 70 m radio telescope, and 21 detections were made; 86 GHz SiO Mopra observations of a subset of the sample are also presented. Of the 21 H 2 O detections, 15 are from sources that are likely to be massive AGB stars and most of these show typical, regular H 2 O maser profiles. In contrast, nearly all the detections of more evolved stars exhibited high-velocity H 2 O maser emission. Of the five sources seen, v223 (W43A, IRAS 18450À0148) is a well-known ''water-fountain'' source that belongs to a small group of post-AGB stars with highly collimated, high-velocity H 2 O maser emission. A second source in our sample, v270 (IRAS 18596+0315), is also known to have high-velocity emission. We report the discovery of similar emission from a further three sources, d46 (IRAS 15445À5449), d62 (IRAS 15544À5332), and b292 (IRAS 18043À2116). The source d46 is an evolved post-AGB star with highly unusual maser properties. The H 2 O maser emission from d62 is probably associated with a massive star. The source b292 is a young post-AGB star that is highly likely to be a water-fountain source, with masers detected over a velocity range of 210 km s À1 .

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Very long baseline interferometric observations of the H20 sources inW49N, W3(OH), ORI A, and VY CMa.

Cited by 39 publications

References 0 publications

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

HERSCHEL/HIFI OBSERVATIONS OF A NEW INTERSTELLAR WATER MASER: THE 5₃₂-4₄₁TRANSITION AT 620.701 GHz

H₂O Maser Observations of Candidate Post‐AGB Stars and Discovery of Three High‐Velocity Water Sources

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Very long baseline interferometric observations of the H20 sources inW49N, W3(OH), ORI A, and VY CMa.

Cited by 39 publications

References 0 publications

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

HERSCHEL/HIFI OBSERVATIONS OF A NEW INTERSTELLAR WATER MASER: THE 532-441TRANSITION AT 620.701 GHz

H2O Maser Observations of Candidate Post‐AGB Stars and Discovery of Three High‐Velocity Water Sources

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HERSCHEL/HIFI OBSERVATIONS OF A NEW INTERSTELLAR WATER MASER: THE 5₃₂-4₄₁TRANSITION AT 620.701 GHz

H₂O Maser Observations of Candidate Post‐AGB Stars and Discovery of Three High‐Velocity Water Sources