Using He I 1083 nm line for coronal magnetometry through the Hanle effect

This investigation presents how the Hanle effect acting on the He I 1083.0 nm line linear polarization signal could be utilized to infer properties of the solar coronal magnetic field. The Hanle effect changes the linear polarization of specific atomic transitions depending on the magnetic field properties. However, the Hanle effect is an effective diagnostic only in a narrow range of magnetic field strengths, dependent on the atomic transition. The He I 1083.0 nm is a unique diagnostic as it is Hanle sensitive to magnetic field strengths observed in the solar corona. Furthermore, the He I 1083 nm line is observed regularly in erupting prominences as we as it has been observed as diffuse emission in the extended corona up to a few solar radii.We present numerical modeling of the of He I 1083 nm linear polarization signals due to the Hanle effect in Low-Hundhausen coronal cavity models as well as in more realistic rMHD models of solar eruptions from Fan (2017). Our results show that the deviation from purely radial linear polarization of the He I 1083 nm line is strongly correlated with the local longitudinal coronal magnetic field. This diagnostic provides a robust measurable of the sign of the longitudinal magnetic field strength. We also present preliminary observational results on the He I 1083 nm line observations from the CHIP and uCOMP observatories in erupting prominences, showing its extended observability throughout the solar corona. The findings presented in this contribution demonstrate the possibility for potential coronal magnetic field diagnostic based on polarimetric measurements with sensitivity on the order of 1e-2. The described approach is complimentary to the coronal magnetometry based on the circular polarization of forbidden coronal lines.