Supernovae and Their Massive Star Progenitors
  I briefly describe the Lick Observatory Supernova Search with the 0.76-m Katzman Automatic Imaging Telescope. I then present an overview of optical observations of Type II, IIb, Ib, and Ic supernovae (SNe), all of which are thought to arise from core collapse in massive progenitors that have previously experienced different amounts of mass loss. SNe IIn are distinguished by relatively narrow emission lines with little or no P-Cygni absorption component; they probably have unusually dense circumstellar gas with which the ejecta interact. Some SNe IIn, however, might actually be super-outbursts of luminous variable stars; rarely, they may even be SNe Ia in disguise. Plausible detections of the progenitors of a few SNe II have been made. Spectropolarimetry of core-collapse SNe reveals that asphericity increases toward the core. 
Alexei V. Filippenko