THE OXYGEN TEMPERATURE OF SN 1987A

The temperature of the oxygen core of SN 1987A is calculated by analyz ing the processes that heat and cool the gas and the processes that fo rm and destroy carbon monoxide. The heating efficiency is calculated b y including the processes by which the energetic electrons created by the radioactive decay of Co-56 lose energy in a mixed gas of O, C, and CO. The effects of nonuniform energy distribution in the supernova ej ecta at early times due to the large optical depths of the gamma-rays are studied by reducing the energy input rate to match the observed em ission of CO. The oxygen core contains a cold CO-emitting region which is effectively cooled by the vibrational emission of CO and heated by the O and C, and a hot O-emitting region which contains neither CO no r SiO and is cooled by the metastable transitions of O. The temperatur e in the CO-emitting region is constant at about 1800 K in the first y ear and drops to 700 K at 800 days, consistent with that derived from the observed spectral shapes of the CO emission. The temperature in th e O-emitting region is relatively high. It ranges from 4800 K at 100 d ays to 2200 K at 800 days, in agreement with that derived from the obs ervations of the [OI] lambda lambda 6300, 6364. The mass of CO predict ed by the thermal-chemical model and the mass derived from the observa tions agree well provided no microscopic mixing of helium is permitted into the oxygen core.