On the inference of magnetic field vectors from Stokes profiles

The range of applicability of the weak-field approximation for the inference of magnetic field vectors is studied from the profiles of the Stokes parameters. It is shown that, for typical solar lines in the visible, this approximation may be applied to an accuracy of ∼ 20% for field strengths as great as 3500/g L G, where g L is the Lande factor, provided that the work is realised in the line wings. A systematic underestimate of the field strength seems to occur for strong fields, observations in several related spectral lines may allow a calibration of this effect, and so for an increase in accuracy of the inferences