A Novel Method to Determine Magnetic Fields in Low-density Plasma Facilitated through Accidental Degeneracy of Quantum States in Fe9+

Li, Wenxian; Grumer, Jon; Yang, Yang; Brage, Tomas; Yao, Ke; Chen, Chongyang; Watanabe, Tetsuya; Jönsson, Per; Lundstedt, Henrik; Hutton, Roger; Zou, Yaming

We propose a new method to determine magnetic fields, by using the magnetic-field-induced electric dipole transition 3p⁴ 3d ⁴D_7/2 to 3p^5 2P_3/2 in Fe⁹⁺ ions. This ion has a high abundance in astrophysical plasma and is therefore well suited for direct measurements of even rather weak fields in, e.g., solar flares. This transition is induced by an external magnetic field and its rate is proportional to the square of the magnetic field strength. We present theoretical values for what we will label the reduced rate and propose that the critical energy difference between the upper level in this transition and the close-to-degenerate 3p⁴3d ⁴D_5/2 should be measured experimentally since it is required to determine the relative intensity of this magnetic line for different magnetic fields.

Article : http://esoads.eso.org/abs/2015ApJ…807…69L