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Monthly Notices of the Royal Astronomical Society


Spectroscopy is presented of the peculiar Type n supernova 1987F, sometimes called the 'Type I Seyfert imposter'. This supernova differed from others of Type n in the slow evolution in its light curve and the strengths and profiles of the spectral lines. The time covered is 1987 April 2 to June 8, when the spectrum of the supernova evolved from a simple nearly featureless blue continuum with superimposed narrow emission lines of H I, He I, [N II], [0 III], and [S II] to a complicated combination of broad and narrow emission components in H I and He I plus the wide features identified by earlier authors as being caused by Fe II. Using a simple model of an expanding spherical shell with absorption for the broad Ha and HP lines, an expansion speed of -8000 km s - 1 is estimated for the outer surface of the shell. This expansion velocity, combined with the mean density of the shell derived three ways, predicts a mass of - 0.2 M0 for the ejected hydrogen above the photosphere. The He abundance appears to be enhanced in this object. The unusual light curve indicates a total luminous energy of -10 51 erg. After 50 d, its shape can be fitted either by a model using a shockwave expanding into circumstellar material, by 56Ni -+ 56CO -+ 56Fe decay with a reddening and radiative transfer dependent mass of 0.8 to 2.6 M0 for the 56Ni, or both. Such a high amount of 56Ni suggests that other mechanisms are involved. Possible processes leading to SN 1987F are explored and the suggested link between this object and AGNs is also briefly discussed.