Two Suggestions to See the Hidden Magnetism of the Solar Chromosphere

TL;DR

This paper discusses how the Hanle effect in specific spectral lines can reveal hidden magnetic fields in the solar chromosphere, beyond what the Zeeman effect can detect, proposing future space-based spectropolarimetric observations.

Contribution

It highlights the potential of using the Ca II IR triplet and He I 10830 Å lines for chromospheric magnetism studies via the Hanle effect with future space telescopes.

Findings

Hanle effect enables detection of magnetic fields invisible to Zeeman effect.

Ca II IR triplet and He I 10830 Å lines are promising for chromospheric magnetism.

Future space telescopes can leverage these lines for advanced solar magnetic field diagnostics.

Abstract

Solar magnetic fields leave their fingerprints in the polarization signatures of the emergent spectral line radiation. This occurs through a variety of rather unfamiliar physical mechanisms, not only via the Zeeman effect. In particular, magnetic fields modify the atomic level polarization (population imbalances and quantum coherences) that anisotropic radiative pumping processes induce in the atoms and molecules of the solar atmosphere. Interestingly, this so-called Hanle effect allows us to "see" magnetic fields to which the Zeeman effect is blind within the limitations of the available instrumentation. Here I argue that the IR triplet of Ca II and the He I 10830 \AA multiplet would be very suitable choices for investigating the magnetism of the solar chromosphere via spectropolarimetric observations from a future space telescope, such as JAXA's SOLAR-C mission.