Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session D13: Nuclear Astrophysics Modelling |
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Sponsoring Units: DNP Chair: Peter Moller, Los Alamos National Laboratory Room: Plaza Court 3 |
Saturday, May 2, 2009 3:30PM - 3:42PM |
D13.00001: ABSTRACT WITHDRAWN |
Saturday, May 2, 2009 3:42PM - 3:54PM |
D13.00002: X-ray Burst Reaction Rate Sensitivities Richard Cyburt Nuclear experimental efforts today are largely driven by the nuclear astrophysics involving exotic nuclei, either on the neutron rich side of stability (r-process) or on the proton rich side of stability (rp-process). In this talk I will discuss the unstable hydrogen and helium burning on the surfaces of neutron stars (rp-process), resulting in Type I X-ray bursts seen by observers. I will present how we ascertain the importance of nuclear reactions in these scenarios and how their variation impacts the X-ray light curves. In the end, this will guide us to where experiment can improve our understanding of these burst events and eventually allow us to constrain neutron star physics. [Preview Abstract] |
Saturday, May 2, 2009 3:54PM - 4:06PM |
D13.00003: Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures Joseph Newton, Richard Longland, Christian Iliadis Reliable reaction rates at high stellar temperatures are necessary for the study of advanced stellar burning stages, supernovae and x-ray bursts. We suggest a new procedure for extrapolating experimental thermonuclear reaction rates to these higher temperatures (T $>$ 1 GK) using statistical model (Hauser-Feshbach) results. Current, generally accepted, procedures involve the use of the Gamow peak, which has been shown to be unreliable for narrow resonances at high stellar temperatures [1]. Our new approach defines the effective thermonuclear energy range (ETER) by using the 8$^{th}$, 50$^{th}$ and 92$^{nd}$ percentiles of the cumulative distribution of fractional resonant reaction contributions. The ETER is then used to define a reliable temperature for matching experimental rates to Hauser-Feshbach rates. The resulting matching temperature is often well above the previous result using the Gamow peak concept. Our new method should provide more accurate extrapolated rates since Hauser-Feshbach rates are more reliable at higher temperatures. These ideas are applied to 21 (p,$\gamma$), (p,$\alpha$) and ($\alpha$,$\gamma$) reactions on a range of A = 20-40 target nuclei and results will be presented. \\[0pt] [1] J.~R.~Newton, C.~Iliadis, A.~E.~Champagne, A.~Coc, Y.~Parpottas and R.~Ugalde, Phys.~Rev.~C 75, 045801 (2007). [Preview Abstract] |
Saturday, May 2, 2009 4:06PM - 4:18PM |
D13.00004: Constraints on Neutron Star Crusts From Oscillations in Giant Flares Andrew Steiner, Anna Watts We show that neutron star seismic modes observed as quasi-periodic oscillations in giant flares emitted by highly-magnetized neutron stars are particularly sensitive to the nuclear physics input of the neutron star crust. In fact, we find that the oscillation frequencies may prove to be one of the strongest constraints from astrophysical observations on the physics of nucleonic matter just below the saturation density. Previous work as suggested that the 30 Hz mode observed is the fundamental crustal mode. We show that this requires a particularly soft nuclear symmetry energy, which may not be supported by planned experimental measurements of the neutron skin thickness of lead. [Preview Abstract] |
Saturday, May 2, 2009 4:18PM - 4:30PM |
D13.00005: Nuclear Gamma-Ray Deexcitation Lines and Continuum from Accelerated-Particle Interactions in Solar Flares Ronald Murphy, Ben-Zion Kozlovsky, Jurgen Kiener, Gerald Share The gamma-ray deexcitation-line production code, developed originally by Ramaty, Kozlovsky and Lingenfelter (1979), has been the primary theoretical tool for analysis of solar-flare gamma-ray data. Analyses using this code have provided information about conditions in flaring magnetic loops, the abundances of the chromosphere where the gamma rays are produced, and the composition and spectrum of the flare- accelerated ions. We have improved its completeness and accuracy in three ways. (1) We use recent line-production cross-section measurements to both improve the included cross sections and to add new cross sections. (2) For the first time, we give a detailed evaluation of the unresolved-line continuum, consisting of all emission not accounted for by the explicit lines addressed by the code. Because adequate laboratory measurements for this emission are not available, the primary tool for this evaluation was the theoretical nuclear program TALYS. (3) We use TALYS to improve those line cross sections where available laboratory measurements are inadequate and to add new, unmeasured cross sections. We also summarize ambient and accelerated-ion composition results from recent analyses of solar-flare data using the improved calculations. [Preview Abstract] |
Saturday, May 2, 2009 4:30PM - 4:42PM |
D13.00006: New results in neutron star crust nucleosynthesis and implications for X-ray Superburst ignition Sanjib Gupta, Peter Moller, Toshihiko Kawano, Daniel Page The heating in neutron star (NS) crusts is due to Electron Capture (EC) and neutron emission/capture reactions. The shallow crustal heating is sensitive to the composition of X-ray burst ashes from explosive burning on the NS surface. Beyond the neutron-drip point the EC-delayed neutron-emissions and resulting neutron-captures onto more tightly bound nuclei drive the composition rapidly toward the cold-catalyzed state, and compositional memory is erased. This has important implications for the thermal conductivity and neutrino emissivity of the inner crust, and also for the thermal profile that results from the nuclear heating. The new nucleosynthesis process deposits a substantial amount of heat very close to neutron-drip (greater than 2 MeV/u). This is in contrast to heating concentrated near the crust-core interface in models relying mostly on pycnonuclear fusion. The new heating location and the erasure of compositional memory directly affect the thermal profiles we can expect for NS that are X-ray Superburst progenitors. The implications for X-ray Superburst ignition by carbon fusion will be discussed. [Preview Abstract] |
Saturday, May 2, 2009 4:42PM - 4:54PM |
D13.00007: ABSTRACT WITHDRAWN |
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