The role of neutrinos in explosive nucleosynthesis in core collapse supernova models with neutrino transport

The problem of core collapse supernova explosions is long standing and attempts to understand the mechanism have been ongoing. On one hand, a full understanding of the underlying mechanism is still pending. On the other hand, there is a need to provide correct nucleosynthesis abundances for the progressing fields of galactic evolution and observations of low-metallicity stars. Traditionally, nucleosynthesis predictions rely on artificially induced explosions which is justifiable for the outer stellar layers but does not account for the effects in the innermost ejecta directly related to the explosion mechanism. The composition of the innermost ejecta is directly linked to the electron fraction Ye = Z/A . This dissertation contains the first investigation of explosive core collapse nucleosynthesis which consistently includes all weak interactions responsible for changes in Ye (neutrino/antineutrino captures on free nucleons and on nuclei, electron/positron captures, and β − /β + -decays). A second novelty of the nucleosynthesis calculations in this thesis is that they are based on core collapse models where the mass cut emerges consistently from the simulation. This is of importance for predicting the amount of Fe-group elements ejected (this is a free parameter in explosions induced by means of a thermal bomb or piston and has to be constrained from observations). Two different approaches are used to achieve explosions (in otherwise non-explosive models): We apply parametrized variations to the neutrino absorption cross sections in order to mimic in one dimension the possible increase of neutrino luminosities caused by uncertainties in proto-neutron star convection in a multi-D scenario. Alternatively, we apply parametrized variations to the neutrino absorption cross section on nucleons in the gain region to mimic the increased neutrino energy deposition which convective turnover of matter in the gain region is expected to provide. We find that both measures lead to explosions and that Ye > 0.5 in the innermost ejected layers (i.e. a proton-rich environment). The nucleosynthesis calculations show that • The proton-rich environment results in enhanced abundances of 45 Sc, 49 Ti, and by chemical evolution studies and observations of low-metallicity stars. • Antineutrino absorption reactions in the proton-rich environment produce neutrons which are immediately captured by neutron-deficient nuclei. • A new nucleosynthesis process (νp-process) takes places in supernovae (and possibly gamma-ray bursts) allowing for appreciable synthesis of elements with mass numbers A > 64. • The νp-process is a candidate for explaining the large Sr abundance seen in a hyper-metal poor star, for the suggested lighter element primary process, and possibly for the origin of the solar abundances of the light p-nuclei

PUSHing Core-Collapse Supernovae to Explosions in Spherical Symmetry: Nucleosynthesis Yields

Core-collapse supernovae (CCSNe) are the extremely energetic deaths of massive stars. They play a vital role in the synthesis and dissemination of many heavy elements in the universe. In the past, CCSN nucleosynthesis calculations have relied on artificial explosion methods that do not adequately capture the physics of the innermost layers of the star. The PUSH method, calibrated against SN1987A, utilizes the energy of heavy-flavor neutrinos emitted by the proto-neutron star (PNS) to trigger parametrized explosions. This makes it possible to follow the consistent evolution of the PNS and to ensure a more accurate treatment of the electron fraction of the ejecta. Here, we present the Iron group nucleosynthesis results for core-collapse supernovae, exploded with PUSH, for two different progenitor series. Comparisons of the calculated yields to observational metal-poor star data are also presented. Nucleosynthesis yields will be calculated for all elements and over a wide range of progenitor masses. These yields can be immensely useful for models of galactic chemical evolution.Comment: 3 pages, 3 figures, poster presentation to appear in the proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC-XIV), Ed. S. Kubono, JPS (Japan Physical Society

Explosion Dynamics of Parametrized Spherically Symmetric Core-Collapse Supernova Simulations

We report on a method, PUSH, for triggering core-collapse supernova (CCSN) explosions of massive stars in spherical symmetry. This method provides a framework to study many important aspects of core collapse supernovae: the effects of the shock passage through the star, explosive supernova nucleosynthesis and the progenitor-remnant connection. Here we give an overview of the method, compare the results to multi-dimensional simulations and investigate the effects of the progenitor and the equation of state on black hole formation.Comment: Proceedings for Nuclei in the Cosmos XIV, Niigata, Japan (2016

Detailed Nucleosynthesis Yields from the Explosion of Massive Stars

Despite the complexity and uncertainties of core collapse supernova simulations there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low metallicity stars. Especially the innermost ejecta are directly affected by the explosion mechanism, i.e. most strongly the yields of Fe-group nuclei for which an induced piston or thermal bomb treatment will not provide the correct yields because the effect of neutrino interactions is not included. Recent observations of metal-poor halo stars support the suggested existence of a lighter element primary process (LEPP) which operates very early in the galaxy and is independent of the r-process. We present a candidate for the LEPP, the so-called νp-proces

Could Failed Supernovae Explain the High r-process Abundances in Some Low Metallicity Stars?

Rapid neutron capture process (r-process) elements have been detected in a large number of metal-poor halo stars. The observed large abundance scatter in these stars suggests that r-process elements have been produced in a site that is rare compared to core-collapse supernovae (CCSNe). Although being rare, neutron star mergers (NSM) alone have difficulties explaining the observations, especially at low metallicities. In this paper, we present a complementary scenario: Using black hole - neutron star mergers (BHNSMs) as additional r-process site. We show that both sites together are able to explain the observed r-process abundances in the Galaxy

White paper on nuclear astrophysics and low energy nuclear physics Part 1: Nuclear astrophysics

This white paper informs the nuclear astrophysics community and funding agencies about the scientific directions and priorities of the field and provides input from this community for the 2015 Nuclear Science Long Range Plan. It summarizes the outcome of the nuclear astrophysics town meeting that was held on August 21–23, 2014 in College Station at the campus of Texas A&M University in preparation of the NSAC Nuclear Science Long Range Plan. It also reflects the outcome of an earlier town meeting of the nuclear astrophysics community organized by the Joint Institute for Nuclear Astrophysics (JINA) on October 9–10, 2012 Detroit, Michigan, with the purpose of developing a vision for nuclear astrophysics in light of the recent NRC decadal surveys in nuclear physics (NP2010) and astronomy (ASTRO2010). The white paper is furthermore informed by the town meeting of the Association of Research at University Nuclear Accelerators (ARUNA) that took place at the University of Notre Dame on June 12–13, 2014. In summary we find that nuclear astrophysics is a modern and vibrant field addressing fundamental science questions at the intersection of nuclear physics and astrophysics. These questions relate to the origin of the elements, the nuclear engines that drive life and death of stars, and the properties of dense matter. A broad range of nuclear accelerator facilities, astronomical observatories, theory efforts, and computational capabilities are needed. With the developments outlined in this white paper, answers to long standing key questions are well within reach in the coming decade