Different geometries of the expanding shell are studied including (1) aspherical envelopes or off-center sources in spherical shells. The size of the polarization observed can be explained by prolate and oblate ellipsoids with axis ratios of about 0.6 and 2, respectively, and/or by the presence of off-center sources which may be produced as a consequence of a close binary evolution. The different geometries are discussed, in particular, distortion of the envelope by an aspherical central explosion, rotation of the progenitor star, and the explosion of a progenitor being member of a close binary system. Based on previous hydrodynamical studies (e.g., Yamada & Sato 1990; Höflich & Steinmetz 1991; Steinmetz & Höflich 1992; Khokhlov 1993) and simple considerations, the most likely configuration for SN 1993J is a binary system in which the progenitor undergoes a common envelope phase or is member in a close system for configuration (1) and (3), respectively.
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P. Hoêflich (1995) studied this question.