Observations of helium and hydrogen emission in quiescent prominences

Illing, R. M. E.; Landman, D. A.; Mickey, D. L.

doi:10.1007/bf00158454

Cited by 49 publications

(51 citation statements)

References 7 publications

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“…3 and 5 have net circular polarization (NCP), i.e., the wavelength integral of the Stokes V profile differs from zero. NCP can only be produced by variations of the magnetic field and velocity along the line-of-sight, which is well known from the early works to explain the broad-band circular polarization in sunspots by Illing et al (1975) and Auer & Heasley (1978) (see, e.g., Sánchez Almeida & Lites 1992, and references therein). This implies that strongly asymmetric Stokes V profiles showing NCP will always be present in sunspots, regardless of the spatial resolution of the observation across the line-of-sight.…”

Section: Discusionmentioning

confidence: 93%

On the origin of reverse polarity patches found byHinodein sunspot penumbrae

Alméida

Ichimoto²

2009

A&A

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Context. The topology of penumbral magnetic fields is poorly known. The satellite Hinode has recently revealed penumbral structures of a magnetic polarity that is opposite to the main sunspot polarity. They may be direct confirmation that magnetic field lines and mass flows return to the solar interior throughout the penumbra, a configuration previously inferred from interpretation of observed Stokes profile asymmetries. Aims. We try to point out the relationship between the reverse polarity features found by Hinode, and the model Micro-Structured Magnetic Atmospheres (MISMAs) proposed for sunspots. Methods. The work is based on synthesis and inversion of sunspot Stokes profiles. Results. Existing model MISMAs produce strongly redshifted reverse polarity structures as found by Hinode. Ad hoc model MISMAs also explain the asymmetric Stokes profiles observed by Hinode. The same modeling may be consistent with magnetograms of dark cored penumbral filaments if the dark cores are associated with the reverse polarity. This hypothetical relationship can only be identified in the far red wings of the spectral lines. Conclusions. The reverse polarity patches may result from aligned magnetic field lines and mass flows that bend over and return to the solar interior throughout the penumbra.

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Section: Discusionmentioning

confidence: 93%

On the origin of reverse polarity patches found byHinodein sunspot penumbrae

Alméida

Ichimoto²

2009

A&A

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“…Lines of sight through the peripheral parts of a flux concentration that expands with height cross its boundary and, in the presence of strong external flows, thus sample significant magnetic field and velocity gradients. As a result, the Stokes-V profiles become asymmetric (Illing et al 1975) with a stronger blue lobe in the case of dominating external downflows (Grossmann-Doerth et al 1988b). The asymmetry arises from the fact that the wavelength shifts due to the Doppler effect and the Zeeman splitting have the same sign for one lobe, but opposite sign for the other lobe.…”

Section: General Propertiesmentioning

confidence: 99%

“…As a result, the Zeeman splitting is smaller and the V-profiles, particularly for the visible line, become strongly asymmetric. Illing et al (1975) have shown that asymmetric Stokes-V profiles arise in the presence of magnetic field and velocity gradients along the line of sight, the sign of the asymmetry being determined by the sign of the product of both gradients. On this basis, a mechanism leading to strongly asymmetric (and unshifted) Stokes-V profiles in the periphery of a static magnetic flux concentration has been suggested by Grossmann-Doerth et al (1988c) and Solanki (1989).…”

Section: Cut Through a Magnetic Featurementioning

confidence: 99%

Stokes diagnostics of simulated solar magneto-convection

Shelyag

Schüßler²,

Solanki³

et al. 2007

A&A

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We present results of synthetic spectro-polarimetric diagnostics of radiative MHD simulations of solar surface convection with magnetic fields. Stokes profiles of Zeeman-sensitive lines of neutral iron in the visible and infrared spectral ranges emerging from the simulated atmosphere have been calculated in order to study their relation to the relevant physical quantities and compare with observational results. We have analyzed the dependence of the Stokes-I line strength and width as well as of the Stokes-V signal and asymmetries on the magnetic field strength. Furthermore, we have evaluated the correspondence between the actual velocities in the simulation with values determined from the Stokes-I (Doppler shift of the centre of gravity) and Stokes-V profiles (zero-crossing shift). We confirm that the line weakening in strong magnetic fields results from a higher temperature (at equal optical depth) in the magnetic flux concentrations. We also confirm that considerable Stokes-V asymmetries originate in the peripheral parts of strong magnetic flux concentrations, where the line of sight cuts through the magnetopause of the expanding flux concentration into the surrounding convective donwflow.

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“…Of special relevance is the asymmetry of the circular polarization profile, which is known to be related to the correlation between velocity and magnetic field gradients along the line-ofsight (LOS; Illing et al 1975). This effect has been exploited to build atmospheric models with such gradients to explain asymmetries around magnetic flux concentrations (Solanki & Pahlke 1988;Grossmann-Doerth et al 1988;Sánchez Almeida et al 1989;Solanki & Montavon 1993).…”

Section: Introductionmentioning

confidence: 99%

Influence of phase-diversity image reconstruction techniques on circular polarization asymmetries

Ramos

González

Khomenko

et al. 2012

A&A

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Context. Full Stokes filter-polarimeters are key instruments for investigating the rapid evolution of magnetic structures on the solar surface. To this end, the image quality is routinely improved using a-posteriori image reconstruction methods. Aims. We analyze the robustness of circular polarization asymmetries to phase-diversity image reconstruction techniques. Methods. We used snapshots of magneto-hydrodynamical simulations carried out with different initial conditions to synthesize spectra of the magnetically sensitive Fe i line at 5250.2 Å. We degraded the synthetic profiles spatially and spectrally to simulate observations with the IMaX full Stokes filter-polarimeter. We also simulated the focused/defocused pairs of images used by the phase-diversity algorithm for reconstruction and the polarimetric modulation scheme. We assume that standard optimization methods are able to infer the projection of the wavefront on the Zernike polynomials with 10% precision. We also consider the less favorable case of 25% precision. We obtain reconstructed monochromatic modulated images that are later demodulated and compared with the original maps. Results. Although asymmetries are often difficult to define in the quiet Sun due to the complexity of the Stokes V profiles, we show how asymmetries are degraded with spatial and spectral smearing. The results indicate that, although image reconstruction techniques reduce the spatial smearing, they can modify the asymmetries of the profiles, which are mainly caused by the appearance of spatiallycorrelated noise.

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Observations of helium and hydrogen emission in quiescent prominences

Cited by 49 publications

References 7 publications

On the origin of reverse polarity patches found byHinodein sunspot penumbrae

On the origin of reverse polarity patches found byHinodein sunspot penumbrae

Stokes diagnostics of simulated solar magneto-convection

Influence of phase-diversity image reconstruction techniques on circular polarization asymmetries

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