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Circular polarization

About: Circular polarization is a research topic. Over the lifetime, 15201 publications have been published within this topic receiving 234418 citations.


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Journal ArticleDOI
01 Jan 1987-Nature
TL;DR: In this paper, the authors reported sensitive measurements of circular polarization in SiO masers associated with late-type stars, which reveal significantly polarized features at the several per cent level in five of six stars observed.
Abstract: Strong SiO masers occur in the inner regions of the stellar envelopes (within a few stellar radii) of variable late-type stars (Miras, semi-regular variables and supergiants), and in the vicinity of IRc2 in Orion, a site of recent star formation. Although linear polarization is a common feature of these masers1–3, previous attempts to detect circular polarization have been inconclusive. Johnson and Clark4 claimed detection of 10–20% polarization in Stokes V (left-hand circular minus right-hand circular) spectra of the Orion masers at 86.2 GHz. Troland et al.1 failed to confirm this result, while reporting small signals in Stokes V spectra for several sources which they attributed to instrumental effects. Here we report sensitive measurements of circular polarization in SiO masers associated with late-type stars, which reveal significantly polarized features at the several per cent level in five of six stars observed. Under the Zeeman splitting hypothesis, these measurements imply magnetic fields in the masing gas in the range 10–100 G. The masers associated with IRc2 in the Orion-KL region were not detected in circular polarization.

65 citations

Journal ArticleDOI
TL;DR: In this paper, the optical response of polarization sensitive materials is studied on the basis of a model in which the materials consist of rod molecules that are oriented in random directions and the photoinduced change of the dielectric tensor is expressed as a function of the electric field in a general form.
Abstract: The optical response of polarization sensitive materials is studied on the basis of a model in which the materials consist of rod molecules that are oriented in random directions. The photoinduced change of the dielectric tensor is expressed as a function of the electric field in a general form. Using this expression, we derive the vectorial coupled wave equations in volume polarization holograms. We discuss the basic properties of polarization holograms.

65 citations

Journal ArticleDOI
TL;DR: In this paper, the pitch angle and helicity of the helical jet magnetic field (B field) were used to predict the expected circular polarization signs for active galactic nuclei (AGN) in the MOJAVE sample.
Abstract: Homan & Lister have recently published circular polarization (CP) detections for 34 objects in the MOJAVE sample - a set of bright, compact active galactic nuclei (AGN) being monitored by the Very Long Baseline Array at 15 GHz. We report the detection of 15-GHz parsec-scale CP in two more AGN (3C 345 and 2231+114), and confirm the MOJAVE detection of CP in 1633+382. It is generally believed that the most likely mechanism for the generation of this CP is Faraday conversion of linear polarization (LP) to CP. A helical jet magnetic field (B field) geometry can facilitate this process - linearly polarized emission from the far side of the jet is converted to CP as it passes through the magnetized plasma at the front side of the jet on its way towards the observer. In this case, the sign of the generated CP is essentially determined by the pitch angle and helicity of the helical B field. We have determined the pitch-angle regimes and helicities of the helical jet B fields in eight AGN for which parsec-scale CP has been detected, and used them to predict the expected CP signs for these AGN if the CP is generated via conversion in these helical fields. We have obtained the intriguing result that our predictions agree with the observed signs in all eight cases, provided that the longitudinal B field components in the jets correspond to south magnetic poles. This clearly non-random pattern demonstrates that the observed CP in AGN is directly associated with the presence of helical jet B fields. These results suggest that helical B fields are ubiquitous in AGN jets.

65 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined the linear polarization of the cosmic background radiation as well as the first measurement of the circular polarization at 9 mm wavelength at eleven declinations and one declination for circular polarization.
Abstract: New data which consist of continued measurements of the linear polarization of the cosmic background radiation as well as the first measurement of the circular polarization are examined. Eleven declinations have been surveyed for linear polarization and one declination for circular polarization, all at 9 mm wavelength. No evidence is found for either a significant linear or circular component with statistical errors on the linear component of 20-60 microK for various models. For linear polarization, a 95 percent confidence level limit of 0.1 mK (0.00003) for an axisymmetric anisotropic model is achieved, while for spherical harmonics through third order, a corresponding limit of 0.2 mK is achieved. For a declination of 37 deg, a limit of 12 mK is placed on the time-varying component and 20 mK on the dc component of the circular polarization at the 95 percent confidence level. At 37 percent declination, the sensitivity per beam patch (7 deg) is 0.2 mK.

65 citations

Journal ArticleDOI
TL;DR: In this paper, phase-resolved observations in all four Stokes parameters of RS CVn star II Peg at two separate epochs were used to reconstruct temperature and magnetic field maps.
Abstract: Magnetic fields are ubiquitous in active cool stars, but they are in general complex and weak. Current Zeeman Doppler imaging (ZDI) studies of cool star magnetic fields chiefly employ circular polarization observations because linear polarization is difficult to detect and requires a more sophisticated radiative transfer modeling to interpret. But it has been shown in previous theoretical studies, and in the observational analyses of magnetic Ap stars, that including linear polarization in the magnetic inversion process makes it possible to correctly recover many otherwise lost or misinterpreted magnetic features. We have obtained phase-resolved observations in all four Stokes parameters of the RS CVn star II Peg at two separate epochs. Here we present temperature and magnetic field maps reconstructed for this star using all four Stokes parameters. This is the very first such ZDI study of a cool active star. Our magnetic inversions reveal a highly structured magnetic field topology for both epochs. The strength of some surface features is doubled or even quadrupled when linear polarization is taken into account. The total magnetic energy of the reconstructed field map also becomes about 2.1–3.5 times higher. The overall complexity is also increased as the field energy is shifted toward higher harmonic modes when four Stokes parameters are used. As a consequence, the potential field extrapolation of the four Stokes parameter ZDI results indicates that magnetic field becomes weaker at a distance of several stellar radii due to a decrease of the large-scale field component.

65 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023384
2022821
2021685
2020927
20191,060
2018968