The Type II supernova 1988Z in MCG + 03-28-022: increasing evidence of interaction of supernova ejecta with a circumstellar wind⋆

Abstract

A set of optical observations of SN 1988Z covering a period of 3 yr from the discovery is presented. The spectrum is characterized at all epochs by strong Balmer emission, without the usual P Cygni absorption component which is typical of SNeII at early stages. Several He I emission lines are also visible. The Ha-alpha luminosity decline is exceptionally slow and cannot be explained by a simple radioactive model, so this object is an ideal candidate for a supernova in which there is interaction of the SN ejecta with a circumstellar wind. A number of unresolved, forbidden emission lines of O III, N II, Ne III, Fe II, Fe III, Fe VII, Fe X, and, tentatively, of Fe XI, A X, and Ca V are identified. Their presence and relative strengths suggest the existence of a shock, which lends further support to the theory of an ejecta-wind interaction.