2005A&A...441..271U

We study time-dependent hydrogen ionization in the atmosphere of SN 1987A during the first month after the supernova explosion. The model includes kinetics of hydrogen ionization and excitation, molecular hydrogen kinetics, and a time-dependent energy balance. The primary strong effect of the time-dependent ionization is the enhanced hydrogen ionization compared to the steady-state model. The time-dependent ionization provides a sufficient population of excited hydrogen levels to account for the observed Hα without invoking the external ⁵⁶Ni. We find that the Ba II 6142Å line in SN 1987A can be reproduced for the LMC barium abundance. This resolves the long-standing problem of the unacceptably high barium overabundance in SN 1987A. The key missing factor responsible for the ``barium problem'' is the time-dependent ionization. The modelling of the Hα profile on day 4.64 indicates the ratio of the kinetic energy to the ejected mass ≃0.83x10⁵⁰erg/M_☉.