Published online by Cambridge University Press: 14 August 2015
Model calculations for the interpretations of the CO bands in the IR are discussed. Spherical symmetry is assumed. Profiles of the physical quantities (i.e. temperature, mass, electron density, abundances, etc.) are given by NLTE models which allow for the representation of observed spectra of supernova 1987A in the optical and near infrared. C and O have to be chosen overabundant by a factor of 25 in the helium-rich layers, or a clumpy density distribution structure of a corresponding factor relative to the mean local value is needed. However, the comparison between the observed forbidden OI line at about 6300 A favours the first interpretation. A factor of about 3 has to be taken into account as uncertainty for the overabundance because of the assumptions of the background model. This implies evidence for strong mixing of the helium rich region with more central layers during the stellar evolution and/or the explosion.