H3+ emission in the ejecta of SN 1987A

We present a chemical and thermal model of the envelope of SN 1987A. We assume that half of the hydrogen envelope is broken into many dense clumps and mixed into the inner region. For a range of densities and energy deposition rates, we find two phases, one with a temperature of about 7000 K and another with a temperature of about 3000 K. We suggest that the H-3(+) features originate in the low-temperature clumps. In them, the cooling is mainly through CO vibrational emission, and the H-3(+) vibrational levels are in LTE. Emission features observed at 3.41 and 3.53 mu m can be reproduced satisfactorily by H-3(+) fundamental band emission at a temperature of 2000 K when absorption by telluric water vapor is taken into account. The model is successful in predicting the dependence on time of the emission features.