Explosive Nucleosynthesis in SN 1987A. II. Composition, Radioactivities, and the Neutron Star Mass

We utilize the 20 M_sun_ model published by Nomoto and Hashimoto in 1988 with a 6 M_sun_ He core in order to perform explosive nucleosynthesis calculations. The employed explosion energy of 10^51^ ergs lies within the uncertainty range inferred from the bolometric light curve. The nucleosynthesis processes and their burning products are discussed in detail. The results are compared with abundances from IR observations of SN 1987A and the average nucleosynthesis expected for Type II supernovae in Galactic chemical evolution. We predict the abundances of long-lived radioactive nuclei and their importance for the late light curve and gamma- ray observations. The position of the mass cut between the neutron star and the ejecta is deduced from the total amount of ejected ^56^Ni (0.07 +/- 0.01 M_sun_). This requires a neutron star with a baryonic mass M_b_ = 1.6 +/- 0.045 M_sun_, which corresponds to a gravitational mass M_g_ = 1.43 +/- 0.05 M_sun_ after subtracting the binding energy of a nonrotating neutron star. This uncertainty range only covers errors in the observed values of ^56^Ni and the explosion energy; uncertainties of the stellar model could increase this value up to M_b_ = 1.7 M_sun_ and M_g_ = 1.52 M_sun_.