BROAD-BAND POLARIMETRY OF SUPERNOVAE - SN 1994D, SN 1994Y, SN 1994AE,SN 1995D AND SN 1995H

We have made polarimetric observations of three Type Ia supernovae (SN Ia's) and two Type II supernovae (SN II's). No significant polarizati on was detected for any of the SN Ia's down to the level of 0.2%, whil e polarization of order 1.0% was detected for the two SN II's 1994Y an d 1995H. A catalog of all the supernovae with polarization data is com piled that shows a distinct trend that all the five SN II's with suffi cient polarimetric data show polarizations at about 1%, while none of the nine SN Ia's in the sample show intrinsic polarization. This syste matic difference in polarization of supernovae, if confirmed, raises m any interesting questions concerning the mechanisms leading to superno va explosions. Our observations enhance the use of SN Ia's as tools fo r determining the distance scale through various techniques but sugges t that one must be very cautious in utilizing Type II for distance det erminations. However, we caution that the link between the asphericity of a supernova and the measured ''intrinsic'' polarization is complic ated by reflected light from the circumstellar material and the interv ening interstellar material, the so-called light echo. This effect may contribute more substantially to SN II's than to SN Ia's. The tight l imits on polarization of SN Ia's may constrain progenitor models with extensive scattering nebulae such as symbiotic stars and other systems of extensive mass loss.