Abstract

Optical photometry of the 'plateau' Type II supernova 1983K extending for nearly a year after outburst is presented. At early epochs the blue luminosity of SN 1983K was approximately two magnitudes greater than that of the prototype of the plateau class, SN 1969L, and was five magnitudes greater than that of SN 1987A in the Large Magellanic Cloud. However, by the onset of the exponential tail phase a few months after outburst, the luminosities of all three supernovae were very similar, implying that nearly identical amounts of Ni-56 were produced through explosive nucleosynthesis. The huge range in initial luminosities observed is most likely due to different preexplosion radii, with the progenitor of 1983K having been the most extended of the three supernovae. Hence, it is unlikely that the progenitor of SN 1983K was a Wolf-Rayet star, in spite of the observed similarity of the premaximum spectrum to such stars.