Nucleosynthesis in Electron Capture Supernovae of Asymptotic Giant Branch Stars

We examine nucleosynthesis in the electron capture supernovae of progenitor asymptotic giant branch stars with an O–Ne–Mg core (with the initial stellar mass of 8.8 M ☉ ). Thermodynamic trajectories for the first 810 ms after core bounce are taken from a recent state-of-the-art hydrodynamic simulation. The presented nucleosynthesis results are characterized by a number of distinct features that are not shared with those of other supernovae from the collapse of stars with iron core (with initial stellar masses of more than 10 M ☉ ). First is the small amount of 56 Ni (0.002–0.004 M ☉ ) in the ejecta, which can be an explanation for the observed properties of faint supernovae such as SNe 2008S and 1997D. In addition, the large Ni/Fe ratio is in reasonable agreement with the spectroscopic result of the Crab nebula (the relic of SN 1054). Second is the large production of 64 Zn, 70 Ge, light p -nuclei ( 74 Se, 78 Kr, 84 Sr, and 92 Mo), and in particular, 90 Zr, which originates from the low Y e (0.46–0.49, the number of electrons per nucleon) ejecta. We find, however, that only a 1%–2% increase of the minimum Y e moderates the overproduction of 90 Zr. In contrast, the production of 64 Zn is fairly robust against a small variation of Y e . This provides the upper limit of the occurrence of this type of events to be about 30% of all core-collapse supernovae.