A Biconically Expanding Flow in W43A Traced by SiO Maser Emission

Imai, Hiroshi; Nakashima, Jun-ichi; Diamond, P. J.; Miyazaki, Akira; Deguchi, Shuji

doi:10.1086/429820

Cited by 45 publications

(59 citation statements)

References 11 publications

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“…v223.-Extreme blue-and redshifted features are present. This star has been imaged previously at OH (1612 MHz), H 2 O (22 GHz), and SiO (43 GHz) maser frequencies ( Imai et al 2002( Imai et al , 2005 confirming the object as a post-AGB source with highvelocity H 2 O jets located outside the shell of OH masers. The H 2 O maser spectrum is highly variable (Likkel et al 1992).…”

Section: Namesupporting

confidence: 62%

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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Section: Namesupporting

confidence: 62%

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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“…Additionally, interferometric observations of the OH maser region of this class of objects have revealed aspherical morphologies with either equatorial or bi-conical distributions (Amiri et al 2011). High-resolution observations of the SiO masers of the post-AGB object W43A indicates a biconical outflow (Imai et al 2005). The bipolar jets observed in waterfountain sources are related to the onset of asymmetric PNe (Sahai & Trauger 1998).…”

Section: Cse Morphology and Magnetic Fieldmentioning

confidence: 94%

“…Cotton et al 2008;Desmurs et al 2007;Imai et al 2005), and as far as we can tell, no high-resolution VLBI observation has been performed to image SiO masers in OH/IR stars. These objects have larger CSEs and much longer periods up to 2000 days than do Mira variables (Herman & Habing 1985b).…”

Section: Introductionmentioning

confidence: 99%

VLBA SiO maser observations of the OH/IR star OH 44.8-2.3: magnetic field and morphology

Amiri

Vlemmings

Kemball

et al. 2012

A&A

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Context. SiO maser emission occurs in the extended atmosphere of evolved stars and can be studied at high angular resolution. As compact, high-brightness components they can be used as important tracers of the dynamics at distances close to the central star. The masers also serve as probes of the evolutionary path from spherically symmetric AGB stars to aspherical PNe. Very long baseline interferometry (VLBI) observations of Mira variables indicate that SiO masers are significantly linearly polarized with linear polarization fractions up to 100%. However, no information is available at high angular resolution for SiO masers in higher mass loss OH/IR stars. Theory indicates a different SiO pumping mechanism in higher mass loss evolved stars. Aims. We extend the VLBI SiO maser studies to OH/IR stars. The observations enable us to understand the SiO pumping mechanisms in higher mass-loss evolved objects and to compare them with Mira variables. Additionally, polarimetric observations of SiO masers help us to understand the magnetic field strength and morphology and to distinguish between conflicting polarization theories. Methods. The 43 GHz SiO maser observations of the OH/IR star OH 44.8-2.3 were performed with the VLBA in full polarization spectral line mode. Auxiliary EVLA observations were performed to allow for the absolute calibration of the polarization angle. The Zeeman splitting was measured by cross correlating the right and left circular polarization spectra, as well as the S-curve fitting. Additionally, we analyzed the 1612 MHz OH maser observations of OH 44.8-2.3 from the VLA archive. Results. The SiO masers of OH 44.8-2.2 form a ring located at ∼5.4 AU around the star. The masers appear to be highly linearly polarized with fractional linear polarization up to 100%. The linear polarization vectors are consistent with a dipole field morphology in this star. We report a tentative detection of circular polarization of ∼0.7% for the brightest maser feature. The magnetic field measured for this feature corresponds to 1.5 ± 0.3 G. Additionally, the distribution of the 1612 MHz OH maser emission could indicate an elongated morphology. Conclusions. The SiO masers in OH 44.8-2.3 exhibit a ring morphology. Even though the central AGB star of OH 44.8-2.3 is expected to be larger than typical Mira variables, the SiO masers occur at a similar distance from the stellar photosphere as Mira variables. The SiO masers and the 1612 MHz OH maser emission suggest a mildly preferred direction of the outflow in the CSE of this star. Significant linear polarization is measured for the SiO region of this star, which could develop from either collisional or radiative pumping. In either case, the observed polarization is also consistent with magnetic field structures along the preferred outflow direction. This could reflect the possible role of the magnetic field in shaping the circumstellar environment of this object. Although we cannot firmly distinguish between the different polarization theories, the derived magnetic...

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“…This morphology can not be explained by the standard spherically expanding shell model for the OH maser shells in evolved stars. The dynamical ages of the H 2 O maser jets of W43A & OH 12.8-0.9 are 90 and 50 yr, respectively (Boboltz & Marvel 2007;Imai et al 2005). We measured a shell size of >1600 AU and the expansion velocity of <15 km s −1 for the OH masers.…”

Section: Discussionmentioning

confidence: 99%

“…The H 2 O maser jet has an outflow velocity of ∼145 km s −1 with 39 • inclination from the plane of the sky (Imai et al 2002). The SiO masers of this source are thought to occur in a shock at the interface between the fast collimating jet and the slow biconical outflow (Imai et al 2005). The spatial distribution of the OH maser region of W43A revealed that the OH masers are located inside the H 2 O maser region.…”

Section: W43amentioning

confidence: 92%

The kinematics and magnetic fields in water-fountain sources based on OH maser observations

Amiri

Vlemmings

Langevelde

2011

A&A

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Context. water-fountain sources are a class of post-AGB objects that exhibit bipolar jet-like structures traced by H 2 O maser emission. The circumstellar envelopes of these objects show deviations from spherical symmetry. While the H 2 O masers originate in a collimated outflow in the polar region, the OH masers may be distributed in the equatorial region or a biconical outflow in the circumstellar shell. Magnetic fields could play an important role in collimating the jet and shaping the circumstellar envelope of these objects. Aims. The aim of this project is to understand the morphology of the OH masers in three water-fountain sources, for which we obtained high-resolution interferometric data. We compare the observational parameters of the spectral profile and spatial distribution with our models in order to constrain the morphology and velocity fields of the OH maser shell. We would also like to understand the role of the magnetic field in shaping the circumstellar envelope of these stars. Methods. We observed the OH masers of three water-fountain sources (OH 12.8-0.9, OH 37.1-0.8, and W43A) in full polarization spectral line mode using the UK Multi-Element Radio Linked Interferometer Network. Additionally, we performed reconstruction models of OH maser shells distributed uniformly in equatorial or biconical outflows and compared them with the OH maser observations.Results. The OH masers of W43A seem to be located in the equatorial region of the circumstellar shell, while for OH 12.8-0.9 the masers are likely distributed in a biconical outflow. We measured magnetic fields of ∼360 μG and ∼29 μG on average for OH 37.1-0.8 and OH 12.8-0.9, respectively. The measured field strengths show that a large-scale magnetic field is present in the circumstellar environment of these stars. Conclusions. Our observations show that the OH maser region of the three water-fountain sources studied in this work show signs of aspherical expansion. Reconstruction of the OH maser distribution of these objects show both biconical and equatorial distributions. Magnetic fields likely play an important role in shaping the OH maser region of water-fountain sources.

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A Biconically Expanding Flow in W43A Traced by SiO Maser Emission

Cited by 45 publications

References 11 publications

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

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

VLBA SiO maser observations of the OH/IR star OH 44.8-2.3: magnetic field and morphology

The kinematics and magnetic fields in water-fountain sources based on OH maser observations

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A Biconically Expanding Flow in W43A Traced by SiO Maser Emission

Cited by 45 publications

References 11 publications

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

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

VLBA SiO maser observations of the OH/IR star OH 44.8-2.3: magnetic field and morphology

The kinematics and magnetic fields in water-fountain sources based on OH maser observations

Contact Info

Product

Resources

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

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