Ultraviolet Emission Lines from Circumstellar Gas Surrounding SN 1987A

Abstract

Discovery in 1987 of narrow emission lines in the ultraviolet spectrum of SN 1987A (WAMSTEKER et al. [1]) provided the first direct evidence for circumstellar gas in the vicinity of the supernova. It was apparent from the outset that an emission line spectrum consisting of N V 1240, N IV] 1485, He II 1640, 0 III] 1664, N III] 1750, and C III] 1909 (see Figure 1) was characteristic of a low density photoionized gas, and could not plausibly arise in the ejecta of the SN 1987A explosion only a few months after the outburst. Analysis of subsequent UV spectra obtained with the IUE satellite have shown the emission lines to be a sensitive probe of the supernova’s circumstellar environment and its progenitor’s evolution. The discovery and initial analysis of these lines is presented and discussed in FRANSSON et al. [2]. In this contribution I review their results and present more recent IUE observations of the emission lines, which allows us to determine the physical size of the circumstellar shell.