The supernova 1983k in NGC 4699 - Clues to the nature of Type II progenitors

Optical spectrographic and photometric observations of the Type II supernova 1983k in NGC 4699 are presented. For the first time, high quality spectra have been obtained of a Type II supernova before it reached maximum light. The first of these, taken nearly 10 days before maximum, showed high-ionization N III and He II emission lines atop a strong blue continuum. Near maximum, the emission lines disappeared, leaving weak H I, He I, and Ca II absorption lines. By a month after maximum, the spectra were dominated by P Cygni-like emission lines of H I, again consistent with a Type II classification. The light curve, which showed a very extended peak, and the absorption lines seen at maximum provide independent evidence that the progenitor of this supernova had an extensive, preexisting circumstellar shell.