HST POLARIZATION OBSERVATIONS OF THE JET OF M87

We present the results of pre-refurbishment HST polarization observati ons of the jet of M 87 taken with the Faint Object Camera in the ultra violet and with the WF/PC-I in the visual. From these observations we produce polarization maps of unprecedentedly high resolution. The stru cture of the projected magnetic field is extremely complex and changes on the smallest observable scales. The degree of polarization increas es from the center toward the edges of the jet where it reaches 60%. A comparison of these images with radio polarization maps shows no meas urable depolarization or Faraday rotation. The morphology of knot D is substantially different in the VLA observations by Owen et al. and th ese HST observations. The measured changes in knot D are inconsistent with proper motions and must be intrinsic to the jet structure. While the magnetic field configuration is remarkably similar at the location s of knots D2 and D3, the magnetic field appears to have changed from parallel to perpendicular at the location of knot D1. These results su ggest that this component is associated with a shock front. Simultaneo us polarization observations are required to determine if the changes in the magnetic structure are due to an intrinsic difference in the ma gnetic field configuration as seen by optical and radio emitting elect rons or to a change of the jet structure, with the appearance of a new component.