Observations of SN 1987A in the mid-infrared.

Mid-IR (5-30 microns) observations of SN 1987A are reviewed. The ionic masses of Co I, Co II, Ni I, Cl I, Ne II and Ni-56 are estimated from the line intensities. It is found that, one year after the explosion, the velocities appropriate to the hydrogenic and ionic regions are about 2000 km/s and 1500 km/s, respectively. An ionization fraction of a few percent is derived for the hydrogen/helium envelope. It is suggested that the appearance of neutral ions at 15 months may indicate that dust formation may be imminent.