Magneto-optical effects in the scattering polarization wings of the Ca I resonance line at 4227 angstroms

Abstract

The linear polarization pattern produced by scattering processes in the Ca I resonance line at 4227 angstroms is a valuable observable for probing the solar atmosphere. Via the Hanle effect, the very significant Q/I and U/I line-center signals are sensitive to the presence of magnetic fields in the lower chromosphere with strengths between 5 and 125 G, approximately. On the other hand, partial frequency redistribution (PRD) produces sizable signals in the wings of the Q/I profile, which have always been thought to be insensitive to the presence of magnetic fields. Interestingly, novel observations of this line revealed a surprising behavior: fully unexpected signals in the wings of the U/I profile and spatial variability in the wings of both Q/I and U/I. Here we show that the magneto-optical (MO) terms of the Stokes-vector transfer equation produce sizable signals in the wings of U/I and a clear sensitivity of the Q/I and U/I wings to the presence of photospheric magnetic fields with strengths similar to those that produce the Hanle effect in the line core. This radiative transfer investigation on the joint action of scattering processes and the Hanle and Zeeman effects should facilitate the development of more reliable techniques for exploring the magnetism of stellar atmospheres. To this end, we can now exploit the circular polarization produced by the Zeeman effect, the magnetic sensitivity caused by the above-mentioned MO effects in the Q/I and U/I wings, and the Hanle effect in the line core.

Accepted for publication in the Astrophysical Journal

References in corpus (5)

• Magnetic Diagnostics of the Solar Chromosphere with the Mg II h-k Lines
• The magnetic sensitivity of the Mg ii k line to the joint action of Hanle, Zeeman and magneto-optical effects
• The transfer of resonance line polarization with partial frequency redistribution in the general Hanle-Zeeman regime
• Center to limb observations and modeling of the Ca I 4227 A line
• Spatio-temporal evolution of Hanle and Zeeman synthetic polarization in a chromospheric spectral line

Cited by in corpus (14)

• The magnetic sensitivity of the resonance and subordinate lines of Mg II in the solar chromosphere
• The effects of three-dimensional radiative transfer on the resonance polarization of the Ca I 4227 $\mathring{\mathrm{A}}$ line
• Modeling the scattering polarization of the solar Ca i 4227 Å line with angle-dependent partial frequency redistribution
• The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields. A radiative transfer code and useful approximations
• Magnetic sensitivity in the wing scattering polarization signals of the hydrogen Lyman-alpha line of the solar disk radiation
• Numerical solutions to linear transfer problems of polarized radiation I. Algebraic formulation and stationary iterative methods
• Polarized Line Formation in Arbitrary Strength Magnetic Fields: the case of a two-level atom with hyperfine structure splitting
• Observational indications of magneto-optical effects in the scattering polarization wings of the Ca I 4227 Å line
• Evidence for the Operation of the Hanle and Magneto-Optical Effects in the Scattering Polarization Signals Observed by CLASP2 Across the Mg II h and k Lines
• Assessment of the CRD approximation for the observer's frame RIII redistribution matrix
• The magnetic sensitivity of the Ca II resonance and subordinate lines in the solar atmosphere
• The potential of the wavelength-integrated scattering polarization of the hydrogen Ly-alpha line for probing the solar chromosphere
• Fast and accurate approximation of the angle-averaged redistribution function for polarized radiation
• The polarization angle in the wings of Ca i 4227: A new observable for diagnosing unresolved photospheric magnetic fields