NUCLEOSYNTHESIS IN ELECTRON CAPTURE SUPERNOVAE OF ASYMPTOTIC GIANT BRANCH STARS

Abstract

We examine nucleosynthesis in the electron capture supernovae of progenitor\nAGB stars with an O-Ne-Mg core (with the initial stellar mass of 8.8 M_\\odot).\nThermodynamic trajectories for the first 810 ms after core bounce are taken\nfrom a recent state-of-the-art hydrodynamic simulation. The presented\nnucleosynthesis results are characterized by a number of distinct features that\nare not shared with those of other supernovae from the collapse of stars with\niron core (with initial stellar masses of more than 10 M_\\odot). First is the\nsmall amount of 56Ni (= 0.002-0.004 M_\\odot) in the ejecta, which can be an\nexplanation for observed properties of faint supernovae such as SNe 2008S and\n1997D. In addition, the large Ni/Fe ratio is in reasonable agreement with the\nspectroscopic result of the Crab nebula (the relic of SN 1054). Second is the\nlarge production of 64Zn, 70Ge, light p-nuclei (74Se, 78Kr, 84Sr, and 92Mo),\nand in particular, 90Zr, which originates from the low Y_e (= 0.46-0.49, the\nnumber of electrons per nucleon) ejecta. We find, however, that only a 1-2%\nincrease of the minimum Y_e moderates the overproduction of 90Zr. In contrast,\nthe production of 64Zn is fairly robust against a small variation of Y_e. This\nprovides the upper limit of the occurrence of this type of events to be about\n30% of all core-collapse supernovae.\n