Evidence for Periodic Modulation of Presupernova Mass Loss from the Progenitor of SN 1979C

Examination of the short-term deviations from the best-fit model light curves for 10 years of measurements on the radio supernova SN 1979C at 20 and 6 cm shows periodic behavior. With an observed period of ~1575 days, model interpretations imply an ~8% modulation of the presupernova stellar wind density on a time scale of ~4000 yr. These observations therefore provide the first direct evidence for the periodic modulation of stellar winds on long time scales. Although any interpretations remain tentative at this point, the mechanism may involve modulation of the mass loss in a stellar wind from the presupernova red supergiant either as a result of pulsational instability or, more likely, by interaction with a massive companion star in a highly eccentric binary orbit, similar to the conditions in the VV Cephei star systems.