W. Hix - Academia.edu (original) (raw)
Papers by W. Hix
We utilize multiple-zone, post-processing element synthesis calculations to determine the impact ... more We utilize multiple-zone, post-processing element synthesis calculations to determine the impact of recent ORNL radioactive ion beam measurements on predictions of novae and X-ray burst simulations. We also assess the correlations between all relevant reaction rates and all synthesized isotopes, and translate nuclear reaction rate uncertainties into abundance prediction uncertainties, via a unique Monte Carlo technique.
We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting d... more We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with relatively high accretion rates such asṀ = 10 M ⊙ /s can produce very neutron rich nuclei that are found in the r process. Disks with more moderate accretion rates can produce copious amounts of Nickel as well as the light elements such as Lithium and Boron. Disks with lower accretion rates such asṀ = 1 M ⊙ /s produce large amounts of Nickel as well as some unusual nuclei such as 49 Ti, 45 Sc, 64 Zn and 92 Mo. This wide array of potential nucleosynthesis products is due to the varying influence of electron neutrinos and antineutrinos emitted from the disk on the neutron-to-proton ratio in the outflow. We use a parameterization for the outflow and discuss our results in terms of entropy and outflow acceleration.
The role of nuclear reactions (strong, weak and electromagnetic) and nuclear structure effects ar... more The role of nuclear reactions (strong, weak and electromagnetic) and nuclear structure effects are discussed in a number of stellar applications. We address fusion cross sections in stellar evolution, neutrino-induced reactions in type II supernovae, electron captures in type Ia supernovae and fission in the r-process. All of this is discussed in the context of nucleosynthesis products and their role in galactic chemical evolution.
With the exception of the Big Bang, responsible for 1,2 H, 3,4 He, and 7 Li, stars act as sources... more With the exception of the Big Bang, responsible for 1,2 H, 3,4 He, and 7 Li, stars act as sources for the composition of the interstellar medium. Cosmic rays are related to the latter and very probably due to acceleration of the mixed interstellar medium by shock waves from supernova remnants. Thus, the understanding of the abundance evolution in the interstellar medium and especially the enrichment of heavy elements, as a function of space and time, is essential. It reflects the history of star formation and the lifetimes of the diverse contributing stellar objects. Therefore, the understanding of the endpoints of stellar evolution is essential as well. These are mainly planetary nebulae and type II/Ib/Ic supernovae as evolutionary endpoints of single stars, but also events in binary systems can contribute, like e.g. supernovae of type Ia, novae and possibly X-ray bursts and neutron star or neutron star -black hole mergers. Despite many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies) is not existing, yet. Their fingerprints, however, seen either in spectra, lightcurves, radioactivities/decay gammarays or in galactic evolution, can help to constrain the composition of their ejecta and related model uncertainties.
We utilize multiple-zone, post-processing element synthesis calculations to determine the impact ... more We utilize multiple-zone, post-processing element synthesis calculations to determine the impact of recent ORNL radioactive ion beam measurements on predictions of novae and X-ray burst simulations. We also assess the correlations between all relevant reaction rates and all synthesized isotopes, and translate nuclear reaction rate uncertainties into abundance prediction uncertainties, via a unique Monte Carlo technique.
We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting d... more We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with relatively high accretion rates such asṀ = 10 M ⊙ /s can produce very neutron rich nuclei that are found in the r process. Disks with more moderate accretion rates can produce copious amounts of Nickel as well as the light elements such as Lithium and Boron. Disks with lower accretion rates such asṀ = 1 M ⊙ /s produce large amounts of Nickel as well as some unusual nuclei such as 49 Ti, 45 Sc, 64 Zn and 92 Mo. This wide array of potential nucleosynthesis products is due to the varying influence of electron neutrinos and antineutrinos emitted from the disk on the neutron-to-proton ratio in the outflow. We use a parameterization for the outflow and discuss our results in terms of entropy and outflow acceleration.
The role of nuclear reactions (strong, weak and electromagnetic) and nuclear structure effects ar... more The role of nuclear reactions (strong, weak and electromagnetic) and nuclear structure effects are discussed in a number of stellar applications. We address fusion cross sections in stellar evolution, neutrino-induced reactions in type II supernovae, electron captures in type Ia supernovae and fission in the r-process. All of this is discussed in the context of nucleosynthesis products and their role in galactic chemical evolution.
With the exception of the Big Bang, responsible for 1,2 H, 3,4 He, and 7 Li, stars act as sources... more With the exception of the Big Bang, responsible for 1,2 H, 3,4 He, and 7 Li, stars act as sources for the composition of the interstellar medium. Cosmic rays are related to the latter and very probably due to acceleration of the mixed interstellar medium by shock waves from supernova remnants. Thus, the understanding of the abundance evolution in the interstellar medium and especially the enrichment of heavy elements, as a function of space and time, is essential. It reflects the history of star formation and the lifetimes of the diverse contributing stellar objects. Therefore, the understanding of the endpoints of stellar evolution is essential as well. These are mainly planetary nebulae and type II/Ib/Ic supernovae as evolutionary endpoints of single stars, but also events in binary systems can contribute, like e.g. supernovae of type Ia, novae and possibly X-ray bursts and neutron star or neutron star -black hole mergers. Despite many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies) is not existing, yet. Their fingerprints, however, seen either in spectra, lightcurves, radioactivities/decay gammarays or in galactic evolution, can help to constrain the composition of their ejecta and related model uncertainties.