THE TYPE-II SUPERNOVA 1988Z IN MCG-28-022 - INCREASING EVIDENCE OF INTERACTION OF SUPERNOVA EJECTA WITH A CIRCUMSTELLAR WIND(03)

We present a set of optical observations of SN 1988Z covering a period of 3 yr from the discovery. This relatively bright supernova shows an unusual photometric behaviour, with broad light curves in the B, V an d R bands resembling those of SN 1987F. The colour evolution is unique , with a slow blueward evolution in the early months, after which it r emains nearly constant. The spectrum is characterized at all epochs by strong Balmer emission, without the usual P Cygni absorption componen t which is typical of SNeII at early stages. Several He I emission lin es are also visible. These lines have a complex structure, with severa l components evolving with time with respect to both width and intensi ty. The H alpha luminosity decline is exceptionally slow and cannot be explained by a simple radioactive model, so this object is an ideal c andidate for a supernova in which there is interaction of the SN eject a with a circumstellar wind. A number of unresolved, forbidden emissio n 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] have been identifie d. Their presence and relative strengths suggest the existence of a sh ock, which gives further support to the theory of an ejecta-wind inter action.