Spectroscopic observations of SN1987a in the LMC
This paper describes the results of optical spectroscopy of SN1987a carried out at Mt John University Observatory on a regular basis since 1987 February 25. Typical spectra are presented in an evolutionary sequence, and velocities of Balmer and selected metallic lines are measured in either emission or absorption. The velocities are interpreted together with the results of photoelectric photometry. The Barnes-Evans relationship has been applied to the photometry to give an angular diameter of the photosphere. The expansion velocity of the photosphere is initially about 3700 km s-1 which is similar to the asymptotic value from weaker absorption lines such as the MgIb line. After 40 days the photosphere appears to expand more slowly and it reaches a maximum size of about 145 A.U. after about 100 days before receding inwards. The photometry and spectroscopy together result in a distance modulus of 18.3 ± 0.2.
Key WordsSupernovae SN1987a optical spectra
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