Temporal evolution of the spectrum of Supernova 1987A

Abstract

A preliminary analysis of the changes in the spectrum of SN 1987A is carried out by means of material collected in the Estación Astrofísica de Bosque Alegre since March 1987. In this first approach to the problem we have used spectra on 103 a-D plates with a dispersion of 123 Å/mm, covering the spectral region between 3800 Å and 6000 Å. The plate resolution is about 2.5 Å. Balmer lines (typical of type II supernovae) are readily identified in SN 1987A and most of the spectral lines show P-Cygni profiles. The changes in the spectrum -such as variations in relative intensity of future shifts- can be easily seen and must be related to changes in the physical conditions of the star's envelope. A remarkable case is that of Hβ line which, moved about 150 Å and 200 Å (absorption and emission, respectively) towards shorter wavelengths by the end of March in about one week's time: this could indicate that the gases ejected became optically thick. The radial velocities determined for different lines are continuously decreasing in absolute value since the outburst, on February. This paper will be published in full length elsewhere.