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[43.05] Ni⁵⁶ Mixing in the Early Expansion Phase of SN 1987A

R.C. Mitchell, E. Baron, D. Branch (University of Oklahoma), P. Lundqvist (Stockholm Observatory), S.I. Blinnikov (Institute of Theoretical and Experimental Physics), P.H. Hauschildt (University of Georgia)

Supernova 1987A provided excellent broad-band photometry and spectroscopic coverage over a wide wavelength range. It is particularly well studied in the very early days of a supernova expansion. It is only in recent years that models of the expanding envelope of a supernova have been of sufficient detail to accurately explain the observed spectra. Good agreements have been found between observed and synthetic spectra for day one, but by day four, substantial discrepancies have been observed. Schmutz~et~al.\ (1990), using various hydrodynamic models, noted that observed Balmer lines were much stronger than predicted, despite the fact that the photospheric temperature had dropped below the ionization threshold. Takeda (1991), using a pure H/He steady-state envelope model in non-LTE, also noted the weakness of the theoretical Balmer lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov et al. (1999). Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of Ni⁵⁶ into the outer envelope is required to maintain strong Balmer lines through day four. Preliminary results suggest an average nickel mass of 10^-8 to 10^-7 solar masses mixed above the line forming region at day four. Once the entire time series has been successfully modeled, we will be able to calculate an accurate distance to SN 1987A.

This work was supported in part by NSF grants AST-9731450 and AST-9417102, NASA grant NAG5-3505, and an IBM SUR grant to the University of Oklahoma. Some of the calculations presented in this poster were performed at the San Diego Supercomputer Center (SDSC), supported by the NSF, and at the National Energy Research Supercomputer Center (NERSC), supported by the U.S. DOE. We thank both these institutions for a generous allocation of computer time.