SPECTRAL-LINE PROFILES OF IRON AND NICKEL IN SUPERNOVA 1987A - EVIDENCE FOR A FRAGMENTED NICKEL BUBBLE

We present line profiles of iron-group elements seen in near-infrared spectra of SN 1987A. The profiles are strikingly different from the observed transitions of other elements, but quite similar to those observed in the mid-infrared transitions of the iron-group elements. We are able to rule out blends, optical depth effects and electron scattering as the source of the distinctive profiles. We propose 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. Dramatic changes in the profiles of these lines were seen about 650 d after the explosion. We cannot attribute these changes entirely to the formation of dust, as has been claimed for similar alterations in optical line profiles. Instead we argue that the abrupt change of the iron-group line profiles is primarily the result of faster cooling of the ejecta on the far hemisphere from Earth. © Royal Astronomical Society.