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Register a new userNucleosynthesis in 2D Core-Collapse Supernovae of 11.2 and 17.0 M$_{odot}$ Progenitors: Implications for Mo and Ru Production
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Core-collapse supernovae are the first polluters of heavy elements in the galactic history. As such, it is important to study the nuclear compositions of their ejecta, and understand their dependence on the progenitor structure (e.g., mass, compactness, metallicity). Here, we present a detailed nucleosynthesis study based on two long-term, two-dimensional core-collapse supernova simulations of a 11.2 M$_{odot}$ and a 17.0 M$_{odot}$ star. We find that in both models nuclei well beyond the iron group (up to $Z approx 44$) can be produced, and discuss in detail also the nucleosynthesis of the p-nuclei $^{92,94}$Mo and $^{96,98}$Ru. While we observe the production of $^{92}$Mo and $^{94}$Mo in slightly neutron-rich conditions in both simulations, $^{96,98}$Ru can only be produced efficiently via the $ u$p-process. Furthermore, the production of Ru in the $ u$p-process heavily depends on the presence of very proton-rich material in the ejecta. This disentanglement of production mechanisms has interesting consequences when comparing to the abundance ratios between these isotopes in the solar system and in presolar grains.
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Knowledge of the progenitors of core-collapse supernovae is a fundamental component in understanding the explosions. The recent progress in finding such stars is reviewed. The minimum initial mass that can produce a supernova has converged to 8 +/- 1 solar masses, from direct detections of red supergiant progenitors of II-P SNe and the most massive white dwarf progenitors, although this value is model dependent. It appears that most type Ibc supernovae arise from moderate mass interacting binaries. The highly energetic, broad-lined Ic supernovae are likely produced by massive, Wolf-Rayet progenitors. There is some evidence to suggest that the majority of massive stars above ~20 solar masses may collapse quietly to black-holes and that the explosions remain undetected. The recent discovery of a class of ultra-bright type II supernovae and the direct detection of some progenitor stars bearing luminous blue variable characteristics suggests some very massive stars do produce highly energetic explosions. The physical mechanism is open to debate and these SNe pose a challenge to stellar evolutionary theory.
Theory holds that a star born with an initial mass between about 8 and 140 times the mass of the Sun will end its life through the catastrophic gravitational collapse of its iron core to a neutron star or black hole. This core collapse process is thought to usually be accompanied by the ejection of the stars envelope as a supernova. This established theory is now being tested observationally, with over three dozen core-collapse supernovae having had the properties of their progenitor stars directly measured through the examination of high-resolution images taken prior to the explosion. Here I review what has been learned from these studies and briefly examine the potential impact on stellar evolution theory, the existence of failed supernovae, and our understanding of the core-collapse explosion mechanism.
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.
We investigate core-collapse supernova (CCSN) nucleosynthesis with self-consistent, axisymmetric (2D) simulations performed using the radiation-hydrodynamics code Chimera. Computational costs have traditionally constrained the evolution of the nuclear composition within multidimensional CCSN models to, at best, a 14-species $alpha$-network capable of tracking only $(alpha,gamma)$ reactions from $^{4}$He to $^{60}$Zn. Such a simplified network limits the ability to accurately evolve detailed composition and neutronization or calculate the nuclear energy generation rate. Lagrangian tracer particles are commonly used to extend the nuclear network evolution by incorporating more realistic networks in post-processing nucleosynthesis calculations. However, limitations such as poor spatial resolution of the tracer particles, inconsistent thermodynamic evolution, including misestimation of expansion timescales, and uncertain determination of the multidimensional mass-cut at the end of the simulation impose uncertainties inherent to this approach. We present a detailed analysis of the impact of such uncertainties for four self-consistent axisymmetric CCSN models initiated from stellar metallicity, non-rotating progenitors of 12 $M_odot$, 15 $M_odot$, 20 $M_odot$, and 25 $M_odot$ and evolved with the smaller $alpha$-network to more than 1 s after the launch of an explosion.
In a previously presented proof-of-principle study, we established a parametrized spherically symmetric explosion method (PUSH) that can reproduce many features of core-collapse supernovae for a wide range of pre-explosion models. The method is based on the neutrino-driven mechanism and follows collapse, bounce and explosion. There are two crucial aspects of our model for nucleosynthesis predictions. First, the mass cut and explosion energy emerge simultaneously from the simulation (determining, for each stellar model, the amount of Fe-group ejecta). Second, the interactions between neutrinos and matter are included consistently (setting the electron fraction of the innermost ejecta). In the present paper, we use the successful explosion models from Ebinger et al. (2018) which include two sets of pre-explosion models at solar metallicity, with combined masses between 10.8 and 120 M$_{odot}$. We perform systematic nucleosynthesis studies and predict detailed isotopic yields. The resulting $^{56}$Ni ejecta are in overall agreement with observationally derived values from normal core-collapse supernovae. The Fe-group yields are also in agreement with derived abundances for metal-poor star HD84937. We also present a comparison of our results with observational trends in alpha element to iron ratios.
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