Evidence for the Zeeman effect in the OH maser emission from W3 /OH/

Moran, J. M.; Reid, M. J.; Lada, Charles J.; Yen, J. L.; Johnston, K. J.; Spencer, J. H.

doi:10.1086/182761

Cited by 48 publications

(26 citation statements)

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“…Of these pairs, 11 are separated by less than 5 mas, while one pair (Z 1 ) has a separation of 13 mas between the RHC and LHC components. All the pairs have V LHC < V RHC , indicating a magnetic field directed away from us, in agreement with previous 6.0‐GHz studies of this source (Moran et al 1978; Desmurs et al 1998).…”

Section: Resultssupporting

confidence: 91%

The association of OH and methanol masers in W3(OH)

Etoka¹,

Cohen²,

Gray³

2005

Monthly Notices of the Royal Astronomical Society

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We present single‐baseline Multi‐Element Radio‐Linked Interferometer Network (MERLIN) measurements of excited OH 6.0‐GHz masers and methanol 6.7‐GHz masers for the source W3(OH). These allow us to compare the positions of individual maser spots of these two species to ∼15 mas accuracy for the first time, and to compare these with previously published positions of ground‐state OH masers near 1.7 GHz and excited‐state OH masers near 4.7 GHz. There is a strong association between OH 6035‐MHz and 1665‐MHz masers. OH and methanol have very similar distributions, but associations of individual masers are relatively rare: most methanol 6.7‐GHz masers are within 100 mas of OH 6.0‐GHz masers, but only four methanol masers are within 15 mas of an OH 6.0‐GHz maser. There are no correspondences of either species with excited OH 4.7‐GHz masers. Zeeman splitting of the 6.0‐GHz OH lines indicates an ordered magnetic field ranging from 3.2 to 14.4 mG. The magnetic fields estimated from co‐propagating masers such as 6035 and 1665 MHz are generally in good agreement with each other.

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Section: Resultssupporting

confidence: 91%

The association of OH and methanol masers in W3(OH)

Etoka¹,

Cohen²,

Gray³

2005

Monthly Notices of the Royal Astronomical Society

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“…The magnetic field strength lies in the range 1 to 10 mG (Desmurs et al, in preparation). Our results confirm the earlier Zeeman measurements made at 6035 MHz by Moran et al (1978). Our new 6031 MHz VLBI maps show a similar spatial distribution and give a value of the field consistent with our 6035 MHz data (Desmurs et al, in preparation;Desmurs, Baudry, & Graham 1997).…”

Section: Resultssupporting

confidence: 91%

“…VLBI observations are needed to search for the spatial coincidence of the two components of a Zeeman pair. We recall that a similar experiment has been done only once in the past (Moran et al 1978) and has never been repeated since then, and we stress that the window around 6-7 GHz is only available with the EVN.…”

Section: Introductionmentioning

confidence: 99%

First EVN Maps of 6-GHz OH Lines in Star Forming Regions

Desmurs¹,

Baudry²

1998

International Astronomical Union Colloquium

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A b s t r a c t . We have used 3 antennas of the EVN to observe in 6 star-forming regions simultaneously, and for the first time, the 2 main lines of the J = | state of OH with right and left circularly polarized feeds. Maser features and Zeeman pairs are identified by searching for emission over adjacent channels, and adjacent positions (within one synthesized beam) in both polarizations after we had mapped and used one selected simple channel as a reference. The magnetic field strength is thus estimated from the Zeeman pairs identified in our OH maps. We briefly present results obtained for W3(OH), ONI, and W51.

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“…The relative absence of 1667 MHz Zeeman pairs with large flux ratios, noted previously in W3(OH) ( Wright et al 2004), is consistent with the picture that maser transitions with smaller Zeeman splitting coefficients tend to have Zeeman pairs in which the -components are more equal in intensity (e.g., Moran et al 1978;Caswell & Vaile 1995). Cook (1966) theorized that correlated velocity and magnetic field gradients could be the cause of unequal spot intensities in Zeeman pairs.…”

Section: Zeeman Pairs and Component Intensitiessupporting

confidence: 86%

Full‐Polarization Observations of OH Masers in Massive Star‐forming Regions. II. Maser Properties and the Interpretation of Polarization

Fish

Reid

2006

ASTROPHYS J SUPPL S

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We analyze full-polarization VLBA data of ground-state OH masers in 18 massive star-forming regions previously presented in a companion paper. We confirm results previously seen in the few individual sources studied at milliarcsecond angular resolution. The OH masers often arise in the shocked neutral gas surrounding ultracompact H ii regions. Magnetic fields as deduced from OH maser Zeeman splitting are highly ordered on the scale of a source and on the maser clustering scale of $10 15 cm, which appears to be universal. OH masers around ultracompact H ii regions live $10 4 yr before turning off abruptly, rather than weakening gradually. These masers have a wide range of polarization properties. At one extreme (e.g., W75 N), -components are detected and the polarization position angles of maser spots show some organization. At the other extreme (e.g., W51 e1/e2), almost no linear polarization is detected and partial depolarization occurs. A typical source has properties intermediate to these two extremes, with no clear pattern in the distribution of polarization position angles. This can be explained if Faraday rotation in a typical OH maser source is large on a maser amplification length but small on a single (e-folding) gain length. Increasing or decreasing Faraday rotation by a factor of $5 among different sources can explain the observed variation in polarization properties. Pure -components (in theory, 100% linearly polarized) are seldom seen. We suggest that almost all -components acquire a significant amount of circular polarization from low-gain stimulated emission of a -component from velocity-coherent OH lying along the propagation path.

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Evidence for the Zeeman effect in the OH maser emission from W3 /OH/

Cited by 48 publications

References 0 publications

The association of OH and methanol masers in W3(OH)

The association of OH and methanol masers in W3(OH)

First EVN Maps of 6-GHz OH Lines in Star Forming Regions

Full‐Polarization Observations of OH Masers in Massive Star‐forming Regions. II. Maser Properties and the Interpretation of Polarization

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