ELECTRON-CAPTURE SUPERNOVAE AS ORIGIN OF 48Ca

We report that electron-capture supernovae (ECSNe), arising from collapsing oxygen-neon-magnesium cores, are a possible source of Ca-48, whose origin has remained a longstanding puzzle. Our two-dimensional, self-consistent explosion model of an ECSN predicts ejection of neutron-rich matter with electron fractions Y-e approximate to 0.40-0.42 and relatively low entropies, s approximate to 13-15 k(B) per nucleon (k(B) is the Boltzmann constant). Post-processing nucleosynthesis calculations result in appreciable production of Ca-48 in such neutron-rich and low-entropy matter during the quasi-nuclear equilibrium and subsequent freezeout phases. The amount of ejected Ca-48 can account for that in the solar inventory when we consider possible uncertainties in the entropies. ECSNe could thus be a site of 48Ca production in addition to a hypothetical, rare class of high-density Type Ia supernovae.