Spectral Line Profiles of Iron and Nickel in Supernova 1987A

Abstract

High resolution (λ/Δλ ~ 1500) near-infrared spectra of SN 1987A taken at the Anglo-Australian Telescope (MEIKLE et al [1], SPYROMILIO et al [2], MEIKLE et al in preparation) show that during the second year after explosion the iron-group line profiles were strikingly different from those of other elements, but were similar to mid-infrared iron-group line profiles (E.F. ERICKSON & M. COHEN private communication). The 1.257 pm [Fe II] and 3.119 µm [Ni I] profiles are compared with Pa β in Fig. 1. The iron group line profiles are characterised by an inflection near the LMC rest wavelength and excess emission red ward of this. We rule out blends, optical depth effects, and electron scattering as the cause of this distinctive shape. We propose instead that the iron-group elements have a unique spatial distribution in the ejecta, and that the profiles were due to emission from a low-density inner region (the nickel bubble) which has fragmented into high-velocity bullets.