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

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

doi:10.1088/0004-637x/737/2/95

Cited by 34 publications

(28 citation statements)

References 31 publications

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“…where θ is the colatitude of the scattered ray. The scattering geometry is shown in Figure 1 of Anusha et al (2011).…”

Section: Polarized Line Transfer Equation With Fstate Interferencementioning

confidence: 99%

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM

Smitha¹,

Nagendra²,

Stenflo³

et al. 2013

ApJ

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Quantum interference effects play a vital role in shaping the linear polarization profiles of solar spectral lines. The Ba ii D 2 line at 4554Å is a prominent example, where the F -state interference effects due to the odd isotopes produce polarization profiles, which are very different from those of the even isotopes that have no F -state interference. It is therefore necessary to account for the contributions from the different isotopes to understand the observed linear polarization profiles of this line. Here we do radiative transfer modeling with partial frequency redistribution (PRD) of such observations while accounting for the interference effects and isotope composition. The Ba ii D 2 polarization profile is found to be strongly governed by the PRD mechanism. We show how a full PRD treatment succeeds in reproducing the observations, while complete frequency redistribution (CRD) alone fails to produce polarization profiles that have any resemblance with the observed ones. However, we also find that the line center polarization is sensitive to the temperature structure of the model atmosphere. To obtain a good fit to the line center peak of the observed Stokes Q/I profile, a small modification of the FALX model atmosphere is needed, by lowering the temperature in the line-forming layers. Because of the pronounced temperature sensitivity of the Ba ii D 2 line it may not be a suitable tool for Hanle magnetic-field diagnostics of the solar chromosphere, because there is currently no straightforward way to separate the temperature and magnetic-field effects from each other.

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“…where θ is the colatitude of the scattered ray. The scattering geometry is shown in Figure 1 of Anusha et al (2011).…”

Section: Polarized Line Transfer Equation With Fstate Interferencementioning

confidence: 99%

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM

Smitha¹,

Nagendra²,

Stenflo³

et al. 2013

ApJ

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“…We have verified by direct numerical computations that this replacement is valid and gives results which are almost identical to the explicit use of type-III redistribution functions. The necessary settings of the branching ratios in order to go to the limit of pure CRD are A = 0 and B (K) = (1 − ǫ) (see also Anusha et al 2011).…”

Section: Polarized Line Transfer Equation For a Two-term Atommentioning

confidence: 99%

J-state interference signatures in the second solar spectrum

Smitha

Nagendra

Stenflo

et al. 2012

A&A

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The scattering polarization in the solar spectrum is traditionally modeled with each spectral line treated separately, but this is generally inadequate for multiplets where J-state interference plays a significant role. Through simultaneous observations of all the 3 lines of a Cr i triplet, combined with realistic radiative transfer modeling of the data, we show that it is necessary to include J-state interference consistently when modeling lines with partially interacting fine structure components. Polarized line formation theory that includes J-state interference effects together with partial frequency redistribution for a two-term atom is used to model the observations. Collisional frequency redistribution is also accounted for. We show that the resonance polarization in the Cr i triplet is strongly affected by the partial frequency redistribution effects in the line core and near wing peaks. The Cr i triplet is quite sensitive to the temperature structure of the photospheric layers. Our complete frequency redistribution calculations in semi-empirical models of the solar atmosphere cannot reproduce the observed near wing polarization or the cross-over of the Stokes Q/I line polarization about the continuum polarization level that is due to the J-state interference. When however partial frequency redistribution is included, a good fit to these features can be achieved. Further, to obtain a good fit to the far wings, a small temperature enhancement of the FALF model in the photospheric layers is necessary.

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“…The ambiguities inherent to magnetic field diagnostics can be reduced by exploiting the joint action of the Hanle and Zeeman effect, where both linear and circular polarization signals are used to constrain the magnetic field vector (Landi Degl'Innocenti & Bommier 1993;Landi Degl'Innocenti 1982;Trujillo Bueno et al 2002;López Ariste & Casini 2003, see also Asensio Ramos et al 2008;Centeno et al 2010;Anusha et al 2011). Unfortunately, while the Lyman-α line is most advantageous to explore the magnetism of the various regions in the transition region (where β ≪ 1), it is challenging to measure the contribution of the Zeeman effect to the circular polarization in UV lines.…”

Section: Introductionmentioning

confidence: 99%

ON THE INVERSION OF THE SCATTERING POLARIZATION AND THE HANLE EFFECT SIGNALS IN THE HYDROGEN Lyα LINE

Ishikawa¹,

Ramos²,

Belluzzi³

et al. 2014

ApJ

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Magnetic field measurements in the upper chromosphere and above, where the gas-to-magnetic pressure ratio β is lower than unity, are essential for understanding the thermal structure and dynamical activity of the solar atmosphere. Recent developments in the theory and numerical modeling of polarization in spectral lines have suggested that information on the magnetic field of the chromospherecorona transition region could be obtained by measuring the linear polarization of the solar disk radiation at the core of the hydrogen Lyman-α line at 121.6 nm, which is produced by scattering processes and the Hanle effect. The Chromospheric Lyman-α Spectropolarimeter (CLASP) sounding rocket experiment aims to measure the intensity (Stokes I) and the linear polarization profiles (Q/I and U/I) of the hydrogen Lyman-α line. In this paper we clarify the information that the Hanle effect can provide by applying a Stokes inversion technique based on a database search. The database contains all theoretical Q/I and U/I profiles calculated in a one-dimensional semi-empirical model of the solar atmosphere for all possible values of the strength, inclination, and azimuth of the magnetic field vector, though this atmospheric region is highly inhomogeneous and dynamic.We focus on understanding the sensitivity of the inversion results to the noise and spectral resolution of the synthetic observations as well as the ambiguities and limitation inherent to the Hanle effect when only the hydrogen Lyman-α is used. We conclude that spectropolarimetric observations with CLASP can indeed be a suitable diagnostic tool for probing the magnetism of the transition region, especially when complemented with information on the magnetic field azimuth that can be obtained from other instruments.

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

Cited by 34 publications

References 31 publications

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM

J-state interference signatures in the second solar spectrum

ON THE INVERSION OF THE SCATTERING POLARIZATION AND THE HANLE EFFECT SIGNALS IN THE HYDROGEN Lyα LINE

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

Cited by 34 publications

References 31 publications

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D24554 Å LINE IN THE SECOND SOLAR SPECTRUM

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D24554 Å LINE IN THE SECOND SOLAR SPECTRUM

J-state interference signatures in the second solar spectrum

ON THE INVERSION OF THE SCATTERING POLARIZATION AND THE HANLE EFFECT SIGNALS IN THE HYDROGEN Lyα LINE

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MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM

MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM