Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session HG: Nuclear Astrophysics: Cosmic Explosions |
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Chair: Sanjay Reddy, Los Alamos National Laboratory Room: Peralta |
Friday, November 5, 2010 10:30AM - 10:42AM |
HG.00001: Investigating the Synthesis of the Primordial Lithium Isotopes Christel Smith, George Fuller, Richard Boyd, Carl Brune The discrepancy between the primordial $^7$Li predicted abundance and the observed abundance in metal poor halo stars has been a longstanding problem. This problem may in fact be coupled with recent observational suggestions that there could be 2-3 orders of magnitude more $^6$Li than Big Bang Nucleosynthesis (BBN) calculations predict. We explore these issues by developing a more comprehensive nuclear reaction network. Some of the nuclear reactions incorporated have not previously been included in BBN calculations and few are well measured in the laboratory. We also discuss the effect of lepton captures on nuclei in BBN and present some calculations. [Preview Abstract] |
Friday, November 5, 2010 10:42AM - 10:54AM |
HG.00002: The Death of the Biggest Stars Alexander Heger, Brian Crosby, Ken Chen The mass of the first generation of stars is still not well constrained from calculations of the first generations of stars; in particular, some theoretical work on the existence of super-massive black holes as seen in quasars at high red shift do call for the formation of super-massive stars as the starting point for those black holes. In this paper we address the question what actually the lives of such stars would be, what is the nucleosynthesis in their interior, what are the different outcomes and mass limits. We will not address the controversial questions how such stars could actually form, but rather take the reverse approach to give us constraints for consequences and outcomes. [Preview Abstract] |
Friday, November 5, 2010 10:54AM - 11:06AM |
HG.00003: Comparison Between Measured and Calculated Gamow-Teller Distributions and the Corresponding Electron Capture Rates for pf-shell Nuclei in Pre-supernova Stars A.L. Cole, T.S. Anderson, R.G.T. Zegers, B.A. Brown, L. Uher, G.W. Hitt Modeling the evolution of core-collapse and thermonuclear supernovae requires determining the electron capture rates on pf-shell nuclei at astrophysical temperatures and densities. We present results of a systematic comparison of electron capture rates determined from experimental Gamow-Teller Strength (B(GT)) distributions to electron capture rates determined from B(GT) distributions calculated with a shell-model code using two different interaction Hamiltonians and from QRPA calculations. The comparisons presented in this work are for 13 stable pf-shell nuclei for which experimentally measured B(GT) distributions have been determined from charge-exchange and beta decay measurements. [Preview Abstract] |
Friday, November 5, 2010 11:06AM - 11:18AM |
HG.00004: New Measurements of the Astrophysically Important $^{44}$Ti Radionuclide Through the $^{40}$Ca($\alpha $,$\gamma )^{44}$Ti Reaction Daniel Robertson, Hans-Werner Becker, Philippe Collon, Joachim Goerres, Michael Wiescher The relatively short-lived radionuclide $^{44}$Ti (t$_{1/2}$=58.9 $\pm$ 0.3 yrs), is of considerable importance in the study of nucleosynthesis in explosive stellar environments. It's production predominantly through the $^{40}$Ca($\alpha $,$\gamma)^{44}$Ti reaction, takes place during $\alpha $-rich freeze-out, in the inner most layers of a core-collapse supernova. A number of experimental studies have been previously performed to determine the stellar reaction rate. These studies included prompt $\gamma $-ray measurements from in-beam experiments, atom counting techniques utilizing accelerator mass spectrometry (AMS) and multi energy step measurements at the DRAGON recoil mass separator. The resulting calculated reaction rates show drastic disagreement. New results from experiments at the DTL, Bochum and NSL, Notre Dame, used both gamma spectroscopy and AMS techniques to measure the reaction, and investigate the discrepancies in both the experimental and predicted results. Final results of the experiments and their impact on the reaction rate will be discussed. [Preview Abstract] |
Friday, November 5, 2010 11:18AM - 11:30AM |
HG.00005: Trends in $^{44}$Ti and $^{56}$Ni from Core-Collapse Supernovae Georgios Magkotsios, Francis Timmes, Aimee Hungerford, Christopher Fryer, Patrick Young, Michael Wiescher We compare the yields of $^{44}$Ti and $^{56}$Ni produced from post-processing the thermodynamic trajectories from three different core-collapse models with the yields from exponential and power-law trajectories. The peak temperatures and densities achieved in these core-collapse models span several of the distinct nucleosynthesis regions we identify, resulting in different trends in the $^{44}$Ti and $^{56}$Ni yields for different mass elements. The $^{44}$Ti and $^{56}$Ni mass fraction profiles from the exponential and power-law profiles generally explain the tendencies of the post-processed yields, depending on which regions are traversed by the model. We also analyze the influence of specific nuclear reactions on the $^{44}$Ti and $^{56}$Ni abundance evolution. Our analysis suggests that not all $^{44}$Ti need be produced in an $\alpha$-rich freeze-out in core-collapse events, and that reaction rate equilibria in combination with timescale effects for the expansion profile may account for the paucity of $^{44}$Ti observed in supernovae remnants. [Preview Abstract] |
Friday, November 5, 2010 11:30AM - 11:42AM |
HG.00006: Neutron Matter Properties and the Neutron Star Mass-Radius Relationship Sanjay Reddy, Joe Carlson, Stefano Gandolfi In the last few years a great effort has been made to constrain the symmetry energy of nuclear matter. Both heavy-ion collision experiments, and accurate mass analysis can be used to measure the symmetry energy, and its derivatives, near saturation density. Simultaneously impressive progress has been made in the astrophysical sector, and the mass/radius relation of neutron stars are starting to be probed in a quantitative way, giving significant constraints on the neutron matter equation of state. In this talk we will show how the symmetry energy of nuclear matter and neutron star properties are strongly correlated in microscopic theories, with connections arising from the three-body force acting between neutrons. Our calculations, based on Quantum Monte Carlo techniques, show how the three-body force constrains both the symmetry energy and neutron star properties so that they are very strongly interconnected. [Preview Abstract] |
Friday, November 5, 2010 11:42AM - 11:54AM |
HG.00007: Constraining phases of quark matter with studies of $r$-mode damping in neutron stars Gautam Rupak, Prashanth Jaikumar We study $r$-mode damping in the color-flavor-locked phase with kaon condensation (CFL-K0) and contrast it with the CFL phase. The mode frequency in these phases are found to differ very slightly. While the bulk viscosity in either phase is only effective at damping the $r$-mode at temperatures $T\ga 10^{11}$K, the shear viscosity in the CFL-K0 phase is the only effective damping agent all the way down to temperatures $T\ga 10^8$K characteristic of cooling neutron stars. However, it cannot keep the star from becoming unstable to gravitational wave emission for rotation frequencies $\nu\approx 56-11$Hz at $T\approx10^8-10^9$K. Stars composed almost entirely of CFL or CFL-K0 matter are ruled out by observation of rapidly rotating neutron stars, indicating that dissipation at the quark-hadron interface or nuclear crust interface must play a key role in damping the instability. [Preview Abstract] |
Friday, November 5, 2010 11:54AM - 12:06PM |
HG.00008: Neutrino cooling and spin-down of rapidly rotating compact stars Prashanth Jaikumar Gravitational radiation destabilizes the $r$-mode in young rapidly rotating compact stars, spinning them down to angular frequencies $\Omega\sim 0.1\Omega_{\rm Kepler}$ soon after their birth in a Supernova. Such quasi-normal pulsation modes are typically expected in the aftermath of a supernova or a sudden rearrangement of the neutron star crust or core. We point out that the $r$-mode perturbation also impacts the neutrino cooling in hot compact stars via processes that restore weak equilibrium. Since the viscous damping timescale is very sensitive to the temperature of the fluid, thermal evolution of the star affects $r$-mode evolution. We illustrate this fact with a simple model of spin-down due to gravitational wave emission in compact stars composed entirely of three-flavor degenerate quark matter. Neutrino cooling of such matter is quantified. Our results imply that a consistent treatment of thermal and spin-frequency evolution of a young and hot compact star is a requisite in estimating the persistence of gravitational waves from such a source. [Preview Abstract] |
Friday, November 5, 2010 12:06PM - 12:18PM |
HG.00009: Detailed Models of Recurring Superbursts from Neutron Stars Laurens Keek, Alexander Heger Superbursts are the most energetic thermonuclear bursts observed from accreting neutron stars. Deep inside the envelope, close to the crust, a thick carbon-rich layer flashes. Afterwards it takes over a day for the neutron star surface to cool down. Because ignition takes place close to the crust, superbursts are sensitive to crustal heating. The amount of crustal heating depends on the nuclear physics in the crust and core, such as the heating processes, thermal conductivity of the crust, and neutrino cooling in the core. Superbursts provide an observational measure to probe this. We present the first multi-zone models of series of recurring superbursts created with a hydrodynamic stellar evolution code that includes a large network of nuclear reactions. We obtain constraints for crustal heating by comparing our models to the scarce observational data. We discuss how our model reproduces characteristics of the observed light curve, such as details of the precursor burst that is seen just prior to the superburst, and the return of normal bursts after an absence caused by the superburst. [Preview Abstract] |
Friday, November 5, 2010 12:18PM - 12:30PM |
HG.00010: ABSTRACT WITHDRAWN |
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