Neutrino-Induced Nucleosynthesis in Helium Shells of Early Core-Collapse Supernovae

¹ School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
² Monash Center for Astrophysics, School of Physics and Astronomy, Monash University, Victoria 3800, Australia
³ Department of Physics, University of California Berkeley, Berkeley, California 94620, USA
⁴ Lawrence Berkeley National Laboratory, Berkeley, California 94620, USA
⁵ Center for Nuclear Astrophysics, INPAC, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, Peoples Republic of China

^a e-mail: banerjee@physics.umn.edu

Published online: 12 February 2016

Abstract

We summarize our studies on neutrino-driven nucleosynthesis in He shells of early core-collapse supernovae with metallicities of Z ≲ 10⁻³ Z_⊙. We find that for progenitors of ∼ 11–15 M_⊙, the neutrons released by ⁴He(_e, e⁺n)³H in He shells can be captured to produce nuclei with mass numbers up to A ∼ 200. This mechanism is sensitive to neutrino emission spectra and flavor oscillations. In addition, we find two new primary mechanisms for neutrino-induced production of 9Be in He shells. The first mechanism produces ⁹Be via ⁷Li(n,γ)⁸Li(n,γ)⁹Li(e⁻ _e)⁹Be and relies on a low explosion energy for its survival. The second mechanism operates in progenitors of ∼ 8 M_⊙, where ⁹Be can be produced directly via ⁷Li(³H, n₀)⁹Be during the rapid expansion of the shocked Heshell material. The light nuclei ⁷Li and ³H involved in these mechanisms are produced by neutrino interactions with ⁴He. We discuss the implications of neutrino-induced nucleosynthesis in He shells for interpreting the elemental abundances in metal-poor stars.