Detailed Spectroscopic Analysis of SN 1987A: The Distance to the Large Magellanic Cloud Using the Spectral‐fitting Expanding Atmosphere Method

Supernova 1987A remains the most well-studied supernova to date. Observationsproduced excellent broad-band photometric and spectroscopic coverage over awide wavelength range at all epochs. We model the observed spectra from Day 1to Day 81 using a hydrodynamical model. We show that good agreement can beobtained at times up to about 60 days, if we allow for extended nickel mixing.Later than about 60 days the observed Balmer lines become stronger than ourmodels can reproduce. We show that this is likely due to a more complicateddistribution of gamma-rays than we allow for in our spherically symmetriccalculations. We present synthetic light curves in UBVRIJHK and a syntheticbolometric light curve. Using this broad baseline of detailed spectroscopicmodels we find a distance modulus mu = 18.5 +/- 0.2 using the SEAM method ofdetermining distances to supernovae. We find that the explosion time agreeswith that of the neutrino burst and is constrained at 68% confidence to within+/- 0.9 days. We argue that the weak Balmer lines of our detailed modelcalculations casts doubt on the accuracy of the purely photometric EPM method.We also suggest that Type IIP supernovae will be most useful as distanceindicators at early times due to a variety of effects.Comment: 47 pages, 29 Figures, to appear in ApJ 574, July 20, 200