The solar abundances of Fe and of the CNO elements play an important role in addressing a number of important issues such as the formation, structure, and evolution of the Sun and the solar system, the origin of the chemical elements, and the evolution of stars and galaxies. Despite the large number of papers published on this issue, debates about the solar abundances of these elements continue. The aim of the present investigation is to quantify the impact of photospheric magnetic fields on the determination of the solar chemical abundances. To this end, we used two 3D snapshot models of the quiet solar photosphere with a different magnetization taken from recent magneto-convection simulations with small-scale dynamo action. Using such 3D models we have carried out spectral synthesis for a large set of Fei, Ci, Ni, and Oi lines, in order to derive abundance corrections caused by the magnetic, Zeeman broadening of the intensity profiles and the magnetically induced changes of the photospheric temperature structure. We find that if the magnetism of the quiet solar photosphere is mainly produced by a small-scale dynamo, then its impact on the determination of the abundances of iron, carbon, nitrogen and oxygen is negligible.

A few years before the Hinode space telescope was launched, an investigation based on the Hanle effect in atomic and molecular lines indicated that the bulk of the quiet solar photosphere is significantly magnetized, due to the ubiquitous presence of an unresolved magnetic field with an average strength 〈B〉, ≈ 130 G. It was pointed out also that this “hidden” field must be much stronger in the intergranular regions of solar surface convection than in the granular regions, and it was suggested that this unresolved magnetic field could perhaps provide the clue for understanding how the outer solar atmosphere is energized. In fact, the ensuing magnetic energy density is so significant that the energy flux estimated using the typical value of 1 km/s for the convective velocity (thinking in rising magnetic loops) or the Alfvén speed (thinking in Alfvén waves generated by magnetic reconnection) turns out to be substantially larger than that required to balance the chromospheric energy losses. Here we present a brief review of the research that led to such conclusions, with emphasis on a new three-dimensional radiative transfer investigation aimed at determining the magnetization of the quiet Sun photosphere from the Hanle effect in the Sr I 4607 Å line and the Zeeman effect in Fe I lines.

Polarized light provides the most reliable source of information at our disposal for diagnosing the physical properties of astrophysical plasmas, including the magnetic fields of the solar atmosphere. The interaction between radiation and hydrogen plus free electrons through Rayleigh and Thomson scattering gives rise to the polarization of the stellar continuous spectrum, which is very sensitive to the medium's thermal and density structure. Anisotropic radiative pumping processes induce population imbalances and quantum coherences among the sublevels of degenerate energy levels (that is, atomic level polarization), which produce polarization in spectral lines without the need of a magnetic field. The Hanle effect caused by the presence of relatively weak magnetic fields modifies the atomic polarization of the upper and lower levels of the spectral lines under consideration, allowing us to detect magnetic fields to which the Zeeman effect is blind. After discussing the physical origin of the polarized radiation in stellar atmospheres, this paper highlights some recent developments in polarized radiation diagnostic methods and a few examples of their application in solar physics.

This paper summarizes the results of a recent investigation on the Hanle effect in atomic and molecular lines, which indicates that there is a vast amount of “hidden” magnetic energy and (unsigned) magnetic flux in the internetwork regions of the quiet solar photosphere. This hidden magnetic energy, localized in the (intergranular) downflowing plasma of the solar photosphere, is carried mainly by tangled fields at sub-resolution scales with strengths between the equipartition field values and ∼1 kG, and is more than sufficient to compensate the radiative energy losses of the solar outer atmosphere.

We report on a novel investigation of the complex magnetism of the quiet Sun which is based on a realistic three-dimensional modeling of the Hanle effect.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html