The Physical Origin of the Scattering Polarization of the Na I D-Lines in the Presence of Weak Magnetic Fields

Abstract

We demonstrate that the atomic alignment of the hyperfine-structure components of the ground level S${}_{1/2}$ of Na {\sc i} and of the upper level P${}_{1/2}$ of the D${}_1$ line are practically negligible for magnetic strengths $B>10\mathrm{G}$, and virtually zero for $B\ga 100 \rm G$. This occurs independently of the magnetic-field inclination on the stellar surface (also, in particular, for vertical fields). Consequently, the characteristic antisymmetric linear-polarization signature of the scattered light in the D${}_1$ line is practically suppressed in the presence of magnetic fields larger than 10 G, regardless of their inclination. Remarkably, we find that the scattering polarization amplitude of the D${}_2$ line increases steadily with the magnetic strength, for vertical fields above 10 G, while the contribution of alignment to the polarization of the D${}_1$ line rapidly decreases. Therefore, we suggest that spectropolarimetric observations of the ``quiet'' solar chromosphere showing significant linear polarization peaks in both D${}_1$ and D${}_2$ cannot be interpreted in terms of one-component magnetic field models, implying that the magnetic structuring of the solar chromosphere could be substantially more complex than previously thought.

11 pages and 2 figures. The Astrophysical Journal Letter (in press)

Cited by in corpus (20)

• A Substantial Amount of Hidden Magnetic Energy in the Quiet Sun
• Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects
• Frequency Redistribution Function for the Polarized Two-Term Atom
• Diagnostics of Coronal Magnetic Fields Through the Hanle Effect in UV and IR Lines
• The impact of quantum interferences between different J-levels on scattering polarization in spectral lines
• The Magnetic Sensitivity of the Ba II D1 and D2 Lines of the Fraunhofer Spectrum
• Dichroic Masers due to Radiation Anisotropy and the Influence of the Hanle Effect on the Circumstellar SiO Polarization
• On the Atomic Polarization of the Ground Level of Na I
• Solving the paradox of the solar sodium D1 line polarization
• Recent Advances in Chromospheric and Coronal Polarization Diagnostics
• A key physical mechanism for understanding the enigmatic linear polarization of the solar BaII and NaI D1 lines
• Depolarizing collisions with hydrogen: neutral and singly ionized alkaline earths
• Radiative transfer modeling of the enigmatic scattering polarization in the solar NaI D1 line
• The physical origin and the diagnostic potential of the scattering polarization in the lithium resonance doublet at 6708 A
• Observations of solar scattering polarization at high spatial resolution
• Physics of polarized scattering at multi-level atomic systems
• Asymmetric shocks in $\chi$ Cyg observed with linear spectropolarimetry
• On the physical origin of the second solar spectrum of the Sc II line at 4247 A
• Collisional effects in modeling solar polarized lines
• Experimental Testing of Scattering Polarization Models