ON SINGULAR POINTS OF THE RADIATION POLAR IZATION TENSOR

The problem of determination of the magnetic field above the chromosph ere from data on the orientation of the vector tau = B-t/B-t can be so lved in various approximations. The direction field 7 is not the only field accessible to observation. The Stokes parameters-components of t he radiation tensor-can be measured at each point in the plane of the sky. The directions of the eigenvectors of this tensor define two orth ogonal systems of integral curves in the plane of the sky. These curve s have singular points, generally of a type different from those in a vector field. It is shown that (1) all first-order singular points are associated with structures observed in the Crab nebula, but the inver se problem for the magnetic field cannot be solved if the synchrotron mechanism is assumed for the radiation; (2) the difference in the pola rization patterns observed with high and low spatial resolution can be explained by the presence of node-saddle associations; (3) the existe nce of singular points with topological indices +/-1/4 is not ruled ou t.