Determination of Direction, Frequency and Polarization of Radio Emission from Galactic OH

Cook, A. H.

doi:10.1038/211503a0

Cited by 36 publications

(27 citation statements)

References 3 publications

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“…Under certain conditions (for instance the matching of the gradients of the velocity and of the magnetic field in the maser region, e.g. Cook (1966) or the overlap of Zeeman components alone) the observed strong polarization is a result of the amplification of one sense of circularly polarized emission. Amplification of only one σ component of the Zeeman pair was postulated in OH maser models (Deguchi & Watson 1986;Elitzur 1996) and can produce high circular polarization up to 100% due to the magnetic beaming (Gray & Field 1994).…”

Section: Discussionmentioning

confidence: 99%

Burst of strongly polarized maser emission at 1612 MHz in the proto-planetary nebula OH17.7–2.0

Szymczak¹,

Gérard²

2005

A&A

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Abstract.We report the discovery of a burst of highly polarized OH maser emission at 1612 MHz in the proto-planetary nebula candidate OH17.7−2.0. The total flux density of two red-shifted features at 72.8 and 73.3 km s −1 increased nearly threefold over a period of ∼430 days. This burst was not associated with any systematic changes of the other 1612 MHz maser features as well as of the 1665 and 1667 MHz masers. The burst was characterized by a linear growth of left-hand circularly polarized emission accompanied by considerable linearly polarized emission. During the burst, the degrees of circular and linear polarization increased up to −80% and 15% respectively. A relation found between the line width and the peak flux density of the two bursting features implies a saturated amplification. Among several possible causes of the burst, a local propagation effect due to Zeeman overlap initiated by evolutionary changes in the shell appears most plausible.

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Section: Discussionmentioning

confidence: 99%

Burst of strongly polarized maser emission at 1612 MHz in the proto-planetary nebula OH17.7–2.0

Szymczak¹,

Gérard²

2005

A&A

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“…Cook (1966) theorized that correlated velocity and magnetic field gradients could be the cause of unequal spot intensities in Zeeman pairs. Deguchi & Watson (1986) argued that even absent a magnetic field gradient, a velocity gradient alone is sufficient to produce unequal intensities.…”

Section: Zeeman Pairs and Component Intensitiesmentioning

confidence: 99%

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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“…In the 1665 and 1667 MHz transitions, the Zeeman splitting is large (0.590 and 0.354 km s −1 mG −1 respectively), and a typical magnetic field of several milligauss will split the two σ-components by many linewidths. Velocity coherence of the amplifying material usually favors one σ-component over the other, resulting in Zeeman pairs of very unequal amplitude or the detection of only a single σ-component (Cook 1966). Since high-mass star-forming regions with OH masers frequently have many masers, including multiple masers at the same velocity, single-dish efforts at identifying maser pairs are generally inadequate.…”

Section: Zeeman Pairsmentioning

confidence: 99%

Enhanced density and magnetic fields in interstellar OH masers

Fish

Reid

Menten

et al. 2006

A&A

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Aims. We have observed the 6030 and 6035 MHz transitions of OH in high-mass star-forming regions to obtain magnetic field estimates in both maser emission and absorption. Methods. Observations were taken with the Effelsberg 100 m telescope. Results. Our observations are consistent with previous results, although we do detect a new 6030 MHz maser feature near −70 km s −1 in the vicinity of W3(OH). In absorption we obtain a possible estimate of −1.1 ± 0.3 mG for the average line-of-sight component of the magnetic field in the absorbing OH gas in K3-50 and submilligauss upper limits for the line-of-sight field strength in DR 21 and W3. Conclusions. These results indicate that the magnetic field strength in the vicinity of OH masers is higher than that of the surrounding, non-masing material, which in turn suggests that the density of masing OH regions is higher than that of their surroundings.

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Determination of Direction, Frequency and Polarization of Radio Emission from Galactic OH

Cited by 36 publications

References 3 publications

Burst of strongly polarized maser emission at 1612 MHz in the proto-planetary nebula OH17.7–2.0

Burst of strongly polarized maser emission at 1612 MHz in the proto-planetary nebula OH17.7–2.0

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

Enhanced density and magnetic fields in interstellar OH masers

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