A new precise measurement of the coronal magnetic field strength

Magnetism dominates the structure and dynamics of the solar corona. Current theories suggest that it may also be responsible for coronal heating. Desp ite the importance of the magnetic field in the physics of the corona and d espite the tremendous progress made recently in the remote sensing of solar magnetic fields, reliable measurements of the coronal magnetic field stren gth and orientation do not exist. This is largely due to the weakness of co ronal magnetic fields, previously estimated to be on the order of 10 G, and the difficulty associated with observing the extremely faint solar corona emission. Using a very sensitive infrared spectropolarimeter to observe the strong near-infrared coronal emission line Fe XIII lambda 10747 above acti ve regions, we have succeeded in measuring the weak Stokes V circular polar ization profiles resulting from the longitudinal Zeeman effect of the magne tic field of the solar corona, From these measurements, we infer field stre ngths of 10 and 33 G from two active regions at heights of h = 0.12 R-circl e dot and h = 0.15 R-circle dot, respectively. We expect that this measurem ent technique will allow, in the near future, the routine precise measureme nt of the coronal magnetic field strength with application to many critical problems in solar coronal physics.