Hanle Coronal Magnetometry Using Permitted He I 1083 nm and Forbidden Si X 1430 nm IR Emission Lines

With a model of the coronal Hanle effect, and by measuring the linear polarization of permitted and forbidden lines, it is possible to determine the magnetic field in the emission region of the considered lines. This technique may be applicable in the corona because of the discovery of faint He I emission, possibly due to a non-equilibrium population of He I atoms originating on coronal dust grains. He I 1083 nm lies in the unsaturated Hanle regime for field strengths below 8 G, so that the polarization amplitude and orientation are sensitive to both the orientation and strength of the magnetic field. To break this degeneracy we can use one of several coronal infrared forbidden lines, like Fe XIII 1075 nm or Si X 1430 nm. These forbidden lines are sensitive to different coronal temperature regimes, and provide additional constraints on the orientation of the magnetic field. We discuss magnetic field uncertainties inherent to this measurement technique, and present the first polarized measurements of the Si X 1430 nm line, obtained using the SOLARC telescope on Haleakalā.