EXTRAORDINARY LINE-EMITTING KNOTS IN THE CRAB-NEBULA

Extraordinary, semistellar, line-emitting knots are apparent in images of the Crab Nebula which were obtained with the Goddard Fabry-Perot imager at the Michigan-Dartmouth-MIT Observatory. The knots are most prominent for [O III] lambda5007 emission through a 5.3 angstrom (FWHM) bandpass centered at 5015.3 angstrom, with representative fluxes of roughly 10(-11) ergs cm-2 s-1. They are aligned in arcs, seven to the north and four to the south, from the pulsar. The northern group appears to be in a bounded corridor through the filamentary structure. Measurements over a 2 year baseline yield proper motions of order 0.1'' yr-1, corresponding to transverse velocities of order 900 km s-1 for a distance of 1830 pc. The knots are characterized by remarkably strong [Ar III] emission, possibly indicating high argon abundances, high gas temperatures, or anomalous physical processes.