Title:
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Ni-56 Mixing in the Outer Layers of SN 1987A

Authors:
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Robert C. Mitchell, E. Baron, David Branch (Oklahoma), Peter Lundqvist 
(Stockholm), Sergei Blinnikov (Moscow), Peter H. Hauschildt (Georgia) & 
Chun S. J. Pun (Goddard)

Abstract:
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Supernova 1987A remains the most well-observed and well-studied
supernova to date. Observations produced excellent broad-band photometric and
spectroscopic coverage over a wide wavelength range at all
epochs. Here, we focus on the very early spectroscopic observations.
Only recently have numerical models
been of sufficient detail to accurately explain the
observed spectra.  In SN 1987A, good agreement has been found between
observed and synthetic spectra for day one, but by day four, the predicted
Balmer lines become much weaker than the observed lines.  We
present the results of work based on a radiation-hydrodynamic model by
Blinnikov and collaborators.  Synthetic
non-LTE spectra generated from this model
by the general radiation transfer code PHOENIX strongly support the
theory that significant mixing of Ni-56 into the outer envelope is
required to maintain strong Balmer lines.
Preliminary results suggest a lower limit to the average nickel mass of
10^{-5} solar masses is required above 5000 km/s by day four.  PHOENIX
models thus have the potential to be a sensitive probe for nickel mixing in 
the outer layers of a supernova.


To appear in:
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ApJ (tentatively the Aug 1, 2001 issue)