Electron Capture Supernovae from Super Asymptotic Giant Branch Stars

Abstract

The 8--10{\thinspace}M ⊙ star forms an electron-degenerate oxygen-neon-magnesium core of ∼ 1.{\thinspace}1{\thinspace}M ⊙ to near Chandrasekhar mass and becomes a super asymptotic giant branch star. Hydrogen and helium shell burning increases the mass of the core, which leads to the contraction of the core. As the central density increases to induce electron capture on24Mg, the core contraction is accelerated. Eventually, electron capture on20Ne ignites Ne and O deflagration, which leads to an electron capture supernovae (ECSNe). Whether the deflagration leads to a direct collapse to form a neutron star or to form a white dwarf by partially ejecting core materials is sensitive to the ignition density and the Ne and O flame propagation speed. We review the presupernova evolution, general hydrodynamics behavior of ECSNe, and show that the collapse is likely to occur in the current evolutionary models, although further study is necessary. We discuss the possible observational signatures of ECSNe, including the light curve model for the Crab supernova 1054.