Modeling the quantum interference signatures of the Ba II D2 4554 A line in the second solar spectrum

Abstract

Quantum interference effects play a vital role in shaping the linear polarization profiles of solar spectral lines. The Ba II D2 line at 4554 A 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 D2 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 D2 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.

Accepted for publication in the Astrophysical Journal

References in corpus (6)

• The Magnetic Sensitivity of the Ba II D1 and D2 Lines of the Fraunhofer Spectrum
• Hanle effect in the solar Ba II D2 line: a diagnostic tool for chromospheric weak magnetic fields
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• Polarized line transfer with F-state interference in a non-magnetic medium: Partial frequency redistribution effects in the collisionless regime
• J-state interference signatures in the Second Solar Spectrum: Modeling the Cr I triplet at 5204-5208 A
• Evidence for collisional depolarization of the \ion{Ba}{ii} $\lambda 4554$ line in the low chromosphere

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• Formal Solutions for Polarized Radiative Transfer. IV. Numerical Performances in Practical Problems
• Polarized scattering with Paschen-Back effect, hyperfine structure, and partial frequency redistribution in magnetized stellar atmospheres
• Polarized Line Formation in Arbitrary Strength Magnetic Fields: the case of a two-level atom with hyperfine structure splitting
• The quantum interference effects in the Sc II 4247 A line of the Second Solar Spectrum