Optical emission from shocks. V - The Magellanic Cloud supernova remnants

High-resolution (velocity resolution of approximately 25 km/s) velocity data on Magellanic Cloud supernova remnants (SNRs) in the forbidden O II doublet obtained with the 3.9-m Anglo-Australian telescope combined with absolute H-alpha photometry obtained with the 1-m telescope at Siding Spring have been shown to be inconsistent with any model requiring the interstellar medium to be homogeneous about, or smoothly varying away from, the explosion center. However, the data do give very strong support to the cloudlet shock model put forward by McKee and coworkers (1975, 1977, 1978). The cloudlets have a mean density around 12 per cu cm and are generally less than a parsec across. The mean kinetic energy deposited by the supernova is in the approximate range log E of 50.3 to 51.3, with a probable value near 7 x 10 to the 50th ergs.