HAZEL (HAnle and ZEeman Light)

Hanle and Zeeman Light is a computer program for the synthesis and inversion of Stokes profiles resulting from the joint action of atomic level polarization and the Hanle and Zeeman effects.

Summary

A big challenge in solar and stellar physics in the coming years will be to decipher the magnetism of the solar outer atmosphere (chromosphere and corona) along with its dynamic coupling with the magnetic fields of the underlying photosphere. To this end, it is important to develop rigorous diagnostic tools for the physical interpretation of spectropolarimetric observations in suitably chosen spectral lines. Here we present a computer program for the synthesis and inversion of Stokes profiles caused by the joint action of atomic level polarization and the Hanle and Zeeman effects in some spectral lines of diagnostic interest, such as those of the He I 1083.0 nm and 587.6 nm (or D₃) multiplets. It is based on the quantum theory of spectral line polarization, which takes into account in a rigorous way all the relevant physical mechanisms and ingredients (optical pumping, atomic level polarization, level crossings and repulsions, Zeeman, Paschen-Back and Hanle effects). The influence of radiative transfer on the emergent spectral line radiation is taken into account through a suitable slab model. The user can either calculate the emergent intensity and polarization for any given magnetic field vector or infer the dynamical and magnetic properties from the observed Stokes profiles via an efficient inversion algorithm based on global optimization methods. This user-friendly diagnostic tool is offered to the astrophysical community, with the hope that it will facilitate new advances in solar and stellar physics.

References

The main reference for the code that you should reference when publishing papers using Hazel is:

• Asensio Ramos, A., Trujillo Bueno, J., Landi Degl’Innocenti, E. 2008, Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects, The Astrophysicsl Journal, 683, 542

Other relevant publications for understanding the physics of polarization of the helium 10830 triplet and the quantum theory of spectral line polarization on which Hazel is based on are:

• Trujillo Bueno, J., Asensio Ramos, A. 2007, Influence of Atomic Polarization and Horizontal Illumination on the Stokes Profiles of the He I 1083.0 nm Multiplet, The Astrophysicsl Journal, 655, 642
• Trujillo Bueno, J., et al. 2002, Selective Absorption Processes and the Origin of Puzzling Spectral Line Polarization from the Sun, Nature, 415, 403
• Trujillo Bueno, J. et al. 2005, The Hanle and Zeeman Effects in Solar Spicules: A Novel Diagnostic Window on Chromospheric Magnetism, The Astrophysical Journal Letters, 619, L191
• Landi Degl'Innocenti, E., & Landolfi, M.,Polarization in Spectral Lines, Astrophysics and Space Science Library, (Springer), 2004

An introductory review paper with a gentle introduction to the Hanle and Zeeman effects is:

• Trujillo Bueno, J. 2005, Quantum Spectropolarimetry and the Sun’s Hidden Magnetism, in “The Dynamic Sun: Challenges for Theory and Observations", ESA SP-600,

Download

The code is freely available to the community, hosted at GitHub. Two versions of the code are available:

• Hazel: original version of the code. Full documentation at http://aasensio.github.io/hazel/
• Hazelv2.0: a complete rewrite of the code, putting emphasis on its usability. The code is now able to synthesize photospheric lines under the assumption of local thermodynamic equilibrium, chromospheric lines under the multi-term approximation (like the He I multiplets) and a selection of arbitrary systematic effects like telluric lines or fringes. Full documentation at https://aasensio.github.io/hazel2/