The 'Seyfert 1' optical spectra of the type II supernovae 1987F and 1988I

Optical spectra of the Type II supernova 1987F, obtained shortly after discovery and at late times, are atypical of SNe II. When first observed, broad Hα was superposed on a nearly featureless continuum, but its profile did not have the characteristic P Cygni shape, and its centroid was blueshifted by >~1500 km s^-1^ with respect to the systemic velocity. Many months later, the object was dominated by broad permitted emission lines of hydrogen, with Fe II and Ca II emission detected as well; forbidden lines, normally quite strong at this phase, were very weak. The derived electron density in the ejected envelope at this time was >~10^9^ cm^-3^. Together with the observed expansion velocities, this leads to an estimate of M>~5-30 M_sun_ for the envelope, implying that the progenitor was very massive. The light curve, which declined very slowly at both early and late times, supports this conclusion. With a few small but possibly significant exceptions, the overall optical spectroscopic properties of SN 1987F closely resemble those of Type I Seyfert nuclei and QSOs; in particular, a comparison is made with the spectrum of 3C 48. The same can be said for the much less extensively observed Type II SN 1988I, although in this object there is no direct evidence for Fe II emission. Even the optical luminosities of the SNe are comparable to those of moderately active galactic nuclei. Had either of these SNe occurred in the nucleus of a normal galaxy, the nucleus would probably have been classified as a Type I Seyfert the only data available were low-resolution optical spectra. It is possible that certain environment conditions, such as the presence of a dense interstellar medium, may increase the rate at which object such as SN 1987F and SN 1988I are produced. Following the work of Terlevich and Melnick, I suggest that the observed properties of some low-luminosity active galaxies might actually be due to violent bursts of star formation rather than accretion onto a supermassive black hole.