Observations of the forward scattering Hanle effect in the Ca I  4227 Å  line

Bianda, M.; Ramelli, R.; Anusha, L. S.; Stenflo, J. O.; Nagendra, K. N.; Holzreuter, R.; Sampoorna, M.; Frisch, H.; Smitha, H. N.

doi:10.1051/0004-6361/201117047

Cited by 19 publications

(19 citation statements)

References 9 publications

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“…The data acquisition was done with the ZIMPOL-3 polarimeter (Ramelli et al 2010) at IRSOL in Switzerland. More observational details are given in Bianda et al (2011). The observations were obtained on 2010 October 15 near the active solar region NOAA 1112 (S19 W5).…”

Section: Observations Of I Q/i U/i and V /I In The Ca I 4227 å Linementioning

confidence: 99%

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ANALYSIS OF THE FORWARD-SCATTERING HANLE EFFECT IN THE Ca I 4227 Å LINE

Anusha

Nagendra

Bianda

et al. 2011

ApJ

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Coherent scattering of limb-darkened radiation is responsible for the generation of the linearly polarized spectrum of the Sun (the Second Solar Spectrum). This Second Solar Spectrum is usually observed near the limb of the Sun, where the polarization amplitudes are largest. At the center of the solar disk the linear polarization is zero for an axially symmetric atmosphere. Any mechanism that breaks the axial symmetry (like the presence of an oriented magnetic field, or resolved inhomogeneities in the atmosphere) can generate a non-zero linear polarization. In the present paper we study the linear polarization near the disk center in a weakly magnetized region, where the axisymmetry is broken. We present polarimetric (I, Q/I , U/I , and V /I) observations of the Ca i 4227 Å line recorded around μ = cos θ = 0.9 (where θ is the heliocentric angle) and a modeling of these observations. The high sensitivity of the instrument (ZIMPOL-3) makes it possible to measure the weak polarimetric signals with great accuracy. The modeling of these high-quality observations requires the solution of the polarized radiative transfer equation in the presence of a magnetic field. For this we use standard one-dimensional model atmospheres. We show that the linear polarization is mainly produced by the Hanle effect (rather than by the transverse Zeeman effect), while the circular polarization is due to the longitudinal Zeeman effect. A unique determination of the full B vector may be achieved when both effects are accounted for. The field strengths required for the simultaneous fitting of Q/I, U/I, and V /I are in the range 10-50 G. The shapes and signs of the Q/I and U/I profiles are highly sensitive to the orientation of the magnetic field.

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Section: Observations Of I Q/i U/i and V /I In The Ca I 4227 å Linementioning

confidence: 99%

“…We have performed new full Stokes profile observations of the Ca i 4227 Å line near the disk center, to explore different regions of varying magnetic activity, from very quiet to moderately active. Details of the observations are given in an accompanying paper (Bianda et al 2011). Here we present an analysis of these observations.…”

Section: Introductionmentioning

confidence: 96%

ANALYSIS OF THE FORWARD-SCATTERING HANLE EFFECT IN THE Ca I 4227 Å LINE

Anusha

Nagendra

Bianda

et al. 2011

ApJ

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“…These observations were performed at IRSOL (Switzerland) using the ZIMPOL-3 polarimeter. For more details on the observations see Bianda et al (2011). Eight different positions along the slit of the spectrograph were selected.…”

Section: The Hanle Effect In the Second Solar Spectrummentioning

confidence: 99%

On the importance of partial frequency redistribution in modeling the scattering polarization

Nagendra

2014

Proc. IAU

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It is well-known that partial frequency redistribution (PRD) is the basic physical mechanism to correctly describe radiative transfer in spectral lines. In the case of polarized line scattering, the PRD becomes particularly important to describe the line-wing polarization, instead of the well-known mechanism of complete redistribution (CRD). Historically, the two-level atom PRD scattering matrices for polarized line scattering were first derived in the 1970's, and later generalized to the case of arbitrary fields in 1997. The latter formulation of the PRD matrices have subsequently been used in the solution of the line transfer equation to successfully model the non-magnetic (resonance scattering) and the magnetic (Hanle scattering) polarization observations. In recent years, using the Kramers-Heisenberg approach, we formulated PRD matrices for various physical mechanisms like quantum interference involving fine- and hyperfine-structure states in a two-term atom. The effect of collisions is included in an approximate way. We have used these PRD matrices to model the observed linear polarization in several interesting lines of the Second Solar Spectrum. In this paper I present a few results which highlight the importance of PRD in the interpretation of the polarized Stokes profiles.

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“…The diagnosis of solar magnetic fields is possible by modeling and understanding the spectral line polarization signals created by scattering processes that result from the matter-radiation interaction. We aim at improving the diagnosis strategies for the chromosphere (namely, for the Ca ii 8542Å line) by investigating the spatial behavior of such scattering polarization when it emerges from the solar disk center, instead of following the usual approach of studying the solar limb (see also Bianda et al 2011;Anusha et al 2011). To understand the differences between both extreme cases we start summarizing the factors affecting the spectral line polarization in a stellar atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Chromospheric diagnosis with forward scattering polarization

Carlin

2014

Proc. IAU

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Is it physically feasible to perform the chromospheric diagnosis using spatial maps of scattering polarization at the solar disk center? To investigate it we synthesized polarization maps (in 8542 Å) resulting from MHD solar models and NLTE radiative transfer calculations that consider Hanle effect and vertical macroscopic motions. After explaining the physical context of forward scattering and presenting our results, we arrive at the definition of Hanle polarity inversion lines. We show how such features can give support for a clearer chromospheric diagnosis in which the magnetic and dynamic effects in the scattering polarization could be disentangled.

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Observations of the forward scattering Hanle effect in the Ca I 4227 Å line

Cited by 19 publications

References 9 publications

ANALYSIS OF THE FORWARD-SCATTERING HANLE EFFECT IN THE Ca I 4227 Å LINE

ANALYSIS OF THE FORWARD-SCATTERING HANLE EFFECT IN THE Ca I 4227 Å LINE

On the importance of partial frequency redistribution in modeling the scattering polarization

Chromospheric diagnosis with forward scattering polarization

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