OPTICAL SPECTROSCOPY OF SUPERNOVA 1987A AT THE AAT .1. THE FORS DATA

We present optical spectra of supernova 1987A, taken during the first 3 yr after the explosion. The spectra cover the 5500-10200-angstrom spectral range with 20-angstrom spectral resolution. The spectrophotometric accuracy of the data is approximately 10 per cent. We propose identifications for most of the prominent features in our spectra and discuss their evolution. We find transitions of H I, He I, C I, O I, Na I, Ca II and the iron group elements. Some identifications are proposed here for the first time. Of particular interest is the absence of the fluoresced 8446-angstrom line of neutral oxygen despite the presence at the same time of the 11287-angstrom line in the same fluorescence cascade. We show that this can be explained by the large optical depth in the line. We find the [C I] lambda-9830 line to be unusually narrow, suggesting little mixing of the carbon-rich region of the progenitor.