Research Activity at IRSOL

IRSOL is a research institute devoted to solar physics. The quality of its instrumentation — result of decades of evolution — allows for unique observations in the field of high precision solar spectropolarimetry.

Presently, the research activities at IRSOL comprise three research foci:

A) observational spectropolarimetry and instrument development,
B) theoretical modeling of the generation and transfer of polarized radiation,
C) numerical simulation of the solar atmosphere and numerical radiative transfer.

The overall goal of the scientific research carried out at IRSOL is the investigation of the physical conditions present in the solar atmosphere, with particular emphasis on its magnetism, and of the physical processes taking place therein. Thanks to the presence of researchers with expertise in each of the three research foci, we can develop synergies to pursue our objectives. Indeed, we can model the intensity and polarization profiles of the radiation emergent from the Sun (research focus B) by exploiting realistic three dimensional simulations of the solar atmosphere (research focus C), and we can finally compare and validate them with the high-quality observations that can be performed with the instrumentation available at IRSOL (research focus A). This “forward modeling” approach provides us with precious information concerning the physical conditions present in the solar atmosphere, the suitability of our modeling assumptions, and the reliability of the atmospheric models developed.

A) Observational spectropolarimetry and instrumentation

The capability of performing worldwide unique spectropolarimetric observations is one of the main reasons of the success of IRSOL. The instrument permitting these observations is the Zurich IMaging POLarimeter, ZIMPOL, originally developed at Institute of Astronomy at ETH Zurich. The instrument evolved significantly and we are now observing with new version ZIMPOL-3 (see reference paper), which was completed at IRSOL in collaboration with SUPSI. We continue working on developing hardware and software improvements of the ZIMPOL-3 system with the goal of exploiting the full potential of current CCD detector technology. The Gregory Coudé telescope at IRSOL and the high resolution spectrograph, are very well suited for spectropolarimetric observations. A Fabry-Perot filter system is also available.

Observational campaigns with ZIMPOL-3 are also organized at external major solar telescopes (e.g GREGOR), in order to obtain observations with high spatial resolution.

B) Theoretical modeling

A large part of the research activity carried out in this research focus concerns the physical mechanisms responsible for the generation and transfer of polarized radiation in the solar atmosphere, as well as the mechanisms through which the magnetic field leaves its imprints in the polarization of the electromagnetic radiation. By taking these mechanisms into account, we model the intensity and polarization profiles of given spectral lines, by solving the radiative transfer problem for polarized radiation in conditions of non-local thermodynamic equilibrium (non-LTE), in realistic models of the solar atmosphere. One of the main goals of this activity is the development of novel diagnostic methods for the investigation of the magnetic fields present in the solar atmosphere, in domains that are not accessible through the conventional techniques (generally based on the Zeeman effect) that are currently applied.

C) Numerical simulations

Presently, we carry out a suite of three-dimensional radiation magnetohydrodynamic simulations of a near-surface section of the Sun, using the computing facilities of the Swiss National Supercomputing Center (CSCS) in Lugano. We carry out the simulation runs with different parameter settings, boundary conditions, and spatial resolution for investigating the small-scale magnetism of the Sun and solar like stars, the turbulent dynamo (believed to operate in the surface layers of the solar convection zone), and the variation of the radiative output in dependence of the magnetic field. Synthetic polarimetric maps from these dynamic model atmospheres are computed for a better understanding of polarimetric measurements and for comparison with observations.

Future numerical simulations are intended to include more physics (heat conduction in addition to radiation, effects of non-ideal fluids, non-equilibrium ionization) for including the still enigmatic outer layers of the solar atmosphere. Of great interest are also larger spatial scales or higher spatial resolution with the intention of shedding light on the working of the solar dynamos and the generation of the small-scale and large-scale magnetic fields.

With these research activities goes the development of numerical methods and codes in radiation magnetohydrodynamics and radiative transfer for the post-processing of the simulation data.