Spectropolarimetric Snapshots of Stripped Envelope Supernovae

Supernovae of Type IIb (SNe IIb) are relatively rare events, constituting roughly 10% of all core-collapse supernovae. However, comparative optical spectroscopy of core-collapse events suggest that SNe IIb represent an important transition from the SNe II to SNe Ib sub-type. SNe IIb progenitors are thought to have been stripped of most, but not all, of their hydrogen envelopes by stellar winds or mass transfer in binary systems. Thus, they provide an opportunity to study the effects of mass-loss on stellar evolution. Spectropolarization signatures of these SNe can provide unique information on the spatial distribution of their ejecta and circumstellar environment/interaction. We present multi-epoch spectropolarimetry of SNe IIb selected from the database of the SNSPOL. The observations were obtained using the SPOL instrument at the University of Arizona telescopes. We analyze the time-dependent spectropolarimetric signatures of the objects in this sample and discuss what these imply about the evolution of the overall geometrical structure of the ejecta and circumstellar material in SNe IIb. These time-dependent "snapshots" provide an important window into stripped-envelope SNe and provide further clues regarding the relationship between SNe IIb and other SNe sub-types.