Freeze out effects and the IR-catastrophe are discussed for SN 1987A and for Type Ia SNe. We show that the light curves of the optical lines in SN 1987A provide strong evidence for the IR-catastrophe. We also argue that most optical lines are dominated by non-thermal excitation after ∼ 800 days. The level of this emission is set mainly by the total mass of the elements. Models of the [OI]λλ6300 – 64 light curve show that an oxygen mass of ∼ 1.5M⊙ is needed. Light curve models for Type Ia SNe display a sharp decrease in the optical flux as a result of the IR-catastrophe at ∼ 500 days, producing UBV-photometry inconsistent with observations of SN 1972E by Kirshner & Oke (1975).

Introduction

Observations of SN 1987A, but also a number of other Type II and Type Ia SNe, at late stages have made it possible to study a number of new features in the evolution of the SN ejecta from explosion to the remnant stage. Here we discuss some recent results in this evolution. A more complete review of the background physics can be found in Fransson (1993).

SN 1987A

It is now well established from the bolometric light curve that ∼ 0.07 M⊙ of 56Ni was created in SN 1987A, and that this is responsible for most of the observed emission from the SN during the first ∼ 800 days. Being based on the bolometric light curve, this is a fairly model independent conclusion.