REMARKS ON THE POLARIZATION OBSERVED IN SN 1993J

Different geometries of the expanding shell are studied including (1) aspherical envelopes or off-center sources in spherical shells. The si ze 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 conse quence of a close binary evolution. The different geometries are discu ssed, in particular, distortion of the envelope by an aspherical centr al explosion, rotation of the progenitor star, and the explosion of a progenitor being member of a close binary system. Based on previous hy drodynamical studies (e.g., Yamada & Sato 1990; Hoflich & Steinmetz 19 91; Steinmetz & Hoflich 1992; Khokhlov 1993) and simple considerations , the most likely configuration for SN 1993J is a binary system in whi ch the progenitor undergoes a common envelope phase or is member in a close system for configuration (1) and (3), respectively.