Presenter:	Javier Trujillo Bueno
Affiliation:	Instituto de Astrofísica de Canarias
Title:	The magnetic sensitivity of the Second Solar Spectrum
Authors:	J. Trujillo Bueno
Form:	invited
Abstract:	The Second Solar Spectrum is a term that was adopted ten years ago by Jan Stenflo and collaborators to refer to the remarkable discovery of the whole spectrum of the ``quiet'' Sun being linearly polarized when observed close to the solar limb -- using a novel polarimeter that allows the detection of very low amplitude fractional polarization signals. This term is certainly adequate because it was indeed as if the Sun had suddenly presented us with an entirely new spectrum to explore. In this talk I review some of the key developments that over the last 10 years have allowed us to go from deciphering the physical origin of several of the enigmatic features of the Second Solar Spectrum to discovering unknown aspects of the Sun's hidden magnetism via sophisticated radiative transfer modeling. The Second Solar Spectrum is the observational signature of coherently superposed quantum states in the atoms and molecules of the solar atmosphere. Magnetic fields break the symmetry of these ``Schr\"odinger's cat states'' giving rise to fascinating observable effects in the emergent spectral line polarization. Interestingly, these effects allow us to ``see'' magnetic fields to which the Zeeman effect is blind within the limitations of the available instrumentation. The magnetic sensitivity of the solar spectrum is thus caused by the Zeeman effect and by a variety of less familiar physical mechanisms by means of which a magnetic field can create and destroy spectral line polarization. I try to show also why the development of suitable instrumentation and novel plasma diagnostic tools for interpreting the Stokes profiles produced by the joint action of the Hanle and Zeeman effects will allow the new generation of solar physicists to achieve new breakthroughs in our empirical understanding of the magnetism of the extended solar atmosphere (photosphere, chromosphere, and corona).
Session:	2. Polarization physics in magnetized media
Presentation date:	Monday 17th September
Presentation time:	14:30:00