Strong effects of time-dependent ionization in early SN 1987A

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
² Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya St. 25, 117259 Moscow, Russia e-mail: utrobin@itep.ru
³ Institute of Astronomy of Russian Academy of Sciences, Pyatnitskaya St. 48, 109017 Moscow, Russia

Received: 22 December 2004
Accepted: 6 June 2005

Abstract

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 6142 Å 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 ≈.