New Spectropolarimetric Diagnostics of Unresolved Magnetic Fields

Shchukina Nataliya, shchukin@mao.kiev.ua, Main Astronomical Observatory (Kiev; Ukraine), Ukraine
Trujillo Bueno Javier, jtb@iac.es, Instituto de Astrofisica de Canarias (Tenerife; Spain)


Abstract
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 Alfven speed (thinking in Alfven waves generated by magnetic reconnection) turns out to be substantially larger than that required to balance the chromospheric energy losses. In the first part of this talk we provide a brief review on the quiet Sun magnetic fields seen by the ``Zeeman eyes" of Hinode, contrasting the results obtained with those that had been found before from ground-based observations. In the second part of the talk, we present 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 460,7 nm line and the Zeeman effect in other atomic lines. Our results indicate that < B > = 160 G in the low photosphere and < B > = 130 G in the upper photosphere. They suggest also that most of the flux and magnetic energy reside on still unresolved scales in the intergranular plasma.