Published online by Cambridge University Press: 25 April 2016
Mt John Observatory photographic spectra of SN 1987A have been obtained on 111 nights during the first year at resolutions of 1.1 Å (blue) and 1.6 Å (red). The early spectra are dominated by broad P Cygni profiles from neutral or singly ionised species. Ba absorption lines may be present. After six months nebular emission features emerged, including [OI] 630, 636 nm and two unidentified UV lines (367, 375 nm) in the previously dark region below 380 nm. Absorption line radial velocities show steep declines in the first month, but are almost constant or only slowly decline after 100 days. For the Hα absorption minimum the initial decline rate was 690 ± 70 km s−1d−1 and the initial velocity was −20.2±0.5 Mm s−1 (LMC frame). By 1988 Feb the slowest material in absorption was at −2.2 Mm s−1.
The emission maxima of Hα and NaID show anomalous redshifts of about 1.0 Mm s−1. The [OI] lines show no such redshift. Recent [OI] and Hα spectra at higher resolution show ‘fine structure’ in the profiles, indicating inhomogeneity in the ejecta. Hβ, Hγ and Hδ (but not Hα) were all weaker or absent from 1987 late March to early May, but strong thereafter. From about 1987 Mar 18 to Apr 17 Hα showed a bump on the blue side of the emission at 647 nm and a double peak (658 and 668 nm). Absorption bumps in the Hα profile in early spectra (1987 Feb) may be due to circumstellar water vapour.