A Qualitative Interpretation of the Second Solar Spectrum of Ce ll

Abstract

This is a theoretical investigation on the formation of the linearly polarized line spectrum of ionized cerium in the sun. We calculate the scattering line polarization pattern emergent from a plane-parallel layer of Ce {\sc ii} atoms illuminated from below by the photospheric radiation field, taking into account the differential pumping induced in the various magnetic sublevels by the anisotropic radiation field. We find that the line polarization pattern calculated with this simple model is in good qualitative agreement with reported observations. Interestingly, the agreement improves when some amount of atomic level depolarization is considered. We find that the best fit to the observations corresponds to the situation where the ground and metastable levels are depolarized to about one fifth of the corresponding value obtained in the absence of any depolarizing mechanism. One possibility to have this situation is that the depolarizing rate value of elastic collisions is exactly $D=10^6{\mathrm{s}}^{-1}$, which is rather unlikely. Therefore, we interpret that fact as} due to the presence of a turbulent magnetic field in the limit of saturated Hanle effect for the lower-levels. For this turbulent magnetic field we obtain a lower limit of 0.8 gauss and an upper limit of 200-300 gauss.

arXiv comment5 pages, 2 figures, to appear in Astron. Astrophys

References in corpus (3)

• The solar chemical composition
• Semi-classical theory of collisional depolarization of spectral lines by atomic hydrogen. I: application to p states of neutral atoms
• Collisional depolarization and transfer rates of spectral lines by atomic hydrogen. IV: application to ionised atoms

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• Hanle effect for stellar dipoles and quadrupoles
• The physical origin and the diagnostic potential of the scattering polarization in the lithium resonance doublet at 6708 A
• Instrumental and Observational Artifacts in Quiet Sun Magnetic Flux Cance llation Functions