Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session FD: Nuclear Astrophysics I |
Hide Abstracts |
Chair: Tohru Motobayashi, RIKEN Room: Kohala 4 |
Friday, October 10, 2014 9:00AM - 9:15AM |
FD.00001: The Fate of Accreted Nuclei in the Neutron Star Inner Crust Alex Deibel, Edward Brown The crust of an accreting neutron star is expected to have a composition that is different from cold-catalyzed matter. The non-equilibrium reactions induced by the accretion of matter gradually transform the ashes of hydrogen and helium burning to neutron-rich matter in the inner crust. These reactions heat and cool the crust, and if the composition is anisotropic, they may produce a mass quadrupole. An important question, then, is how much the composition can vary in the inner crust. We examine this question by using nuclear mass models to investigate the stability of nuclei that must co-exist with degenerate electron and neutron gases. We show that there are few stable nuclei deep in the inner crust, and that the accreted inner crust does not contain equilibrium nuclei. We compare our multicomponent composition results with a full reaction network that includes finite electron and neutron capture reaction rates and pycnonuclear reactions. [Preview Abstract] |
Friday, October 10, 2014 9:15AM - 9:30AM |
FD.00002: MINBAR: A comprehensive study of 6000+ thermonuclear shell flashes from neutron stars Duncan Galloway, Jean in 't Zand, J\'er\^ome Chenevez, Laurens Keek, Celia Sanchez-Fernandez, Erik Kuulkers, Hauke Worpel, Nathanael Lampe Thermonuclear (type-I) X-ray bursts have been observed from accreting neutron stars since the early 1970s. These events serve as a valuable diagnostic tool to constrain the source distance; accretion rate; accreted fuel composition, and hence evolutionary status of the donor; and even the neutron star mass and radius. Additionally, large samples of bursts can serve to test models describing ignition and burning, and hence constrain the nuclear processes taking place. The Multi-INstrument Burst ARchive (MINBAR) is an effort to combine large samples of burst observations from {\it BeppoSAX}/WFC, {\it RXTE}/PCA, and {\it INTEGRAL}/JEM-X. We have searched observations of the approximately 100 known X-ray burst sources, and have accumulated more than 6000 events from 83 sources over the past 20 years. We describe the assembly of the catalogue, the analysis procedures, and the science outcomes and prospects. Notable results so far include a systematic analysis of short recurrence time bursts; evidence for accretion rate variation during bursts; studies of the burst behaviour of new transients; and long-duration bursts including super bursts. [Preview Abstract] |
Friday, October 10, 2014 9:30AM - 9:45AM |
FD.00003: Effects of Magnetic Field and Rotation on $^3P_2$ Superfluidity in Neutron Stars Kota Masuda, Muneto Nitta It is believed that an anisotropic $^3P_2$ superfluid state is realized in the core of neutron stars. Historically, a lot of works (Anderson et. al.(1961), Hoffberg et. al.(1970) and Tamagaki(1970)) discussed the properties of $^3P_2$ superfluid state. Ginzburg-Landau (GL) equation was derived by Fujita, Tsuneto (1972) and Richardson (1972). After that, Mermin (1974) solved the problem of minimizing GL free energy density for d-wave pairing and showed what ground states are realized. By using these results, Sauls and Serene (1978) concluded that the unitary phase is realized in BCS limit, and Sauls et. al. (1982) showed $^3P_2$ vortices have a spontaneous magnetization. In this presentation, we firstly introduce GL equation and show some analogy to that of spin2-BEC. In BCS limit, degenerate ground states are parameterized by one parameter. We show effects of gradient terms, magnetic field and rotation on ground states and half-quantized $^3P_2$ vortices are the most stable states under certain conditions. Next, by using an anisotropic GL equation, we discuss a spontaneous magnetization caused by half-quantized $^3P_2$ vortices and compare results with that of integer vortices. Finally, we comment on possible effects of $^3P_2$ superfluid state on neutron star observables. [Preview Abstract] |
Friday, October 10, 2014 9:45AM - 10:00AM |
FD.00004: Deformed neutron stars due to strong magnetic field in terms of relativistic mean field theories Kota Yanase, Naotaka Yoshinaga Some observations suggest that magnetic field intensity of neutron stars that have particularly strong magnetic field, magnetars, reaches values up to 10$^{\mathrm{14-15}}$G. It is expected that there exists more strong magnetic field of several orders of magnitude in the interior of such stars. Neutron star matter is so affected by magnetic fields caused by intrinsic magnetic moments and electric charges of baryons that masses of neutron stars calculated by using Tolman-Oppenheimer-Volkoff equation is therefore modified. We calculate equation of state (EOS) in density-dependent magnetic field by using sigma-omega-rho model that can reproduce properties of stable nuclear matter in laboratory Furthermore we calculate modified masses of deformed neutron stars. [Preview Abstract] |
Friday, October 10, 2014 10:00AM - 10:15AM |
FD.00005: Charged-current reactions in the supernova neutrino-sphere Jeremy Holt, Ermal Rrapaj, Alexander Bartl, Sanjay Reddy, Achim Schwenk We compute neutrino absorption rates due to charged-current reactions $\nu_e+n \rightarrow e^- + p $ and $\bar{\nu}_e+p \rightarrow e^+ + n$ in the outer regions of a newly born neutron star called the neutrino-sphere. Using realistic nucleon-nucleon potentials that fit measured scattering phase shifts, we calculate the momentum-, density- and temperature-dependent nucleon self-energies in the Hartree-Fock approximation, which leads to an enhancement of the $\nu_e$ cross-section and a suppression of the $\bar{\nu}_e$ cross section. A potential based on chiral effective field theory and a pseudo-potential constructed to reproduce nucleon-nucleon phase shifts are employed. The effect of Hartree-Fock corrections to the nucleon self-energies on the equilibrium proton/electron fraction, and on the charged current rates is studied in detail. We find that for typical ambient conditions in the neutrino-sphere ($T=5-10$ MeV and $\rho =10^{11}-10^{13}$ g/cm$^3$) the difference between the $\nu_{e}$ and $\bar{\nu}_e$ absorption rates are not as large as in previous calculations. Our results have implications for heavy element nucleosynthesis in supernovae and supernova neutrino detection. [Preview Abstract] |
Friday, October 10, 2014 10:15AM - 10:30AM |
FD.00006: Roles of fission, Neutron Star Mergers and Supernovae in R-Process Nucleosynthesis Shota Shibagaki, Toshitaka Kajino, Satoshi Chiba, Grant Mathews The astrophysical site for the r-process has not yet been uniquely identified. Neutron star mergers (NSMs) have recently received special attention as production sites for the r-process. The ejected matter from the NSMs is extremely neutron-rich (Ye\textless 0.1) and the r-process path proceeds along the neutron drip line and enters the region of fissile nuclei. In this situation, theoretical models of nuclear masses and fission are important. In this study, we carry out r-process nucleosynthesis simulations in the NSMs. We constructed a nuclear reaction network code by setting new models of nuclear masses and fission. Our result shows that the final r-process elemental abundances exhibit flat pattern for A$=$90-180 due to several fission cycling in extremely neutron-rich conditions of the NSMs. Combining these results with magnetorotaionally driven core-collapse supernovae (CCSNe) that predict successful r-process abundance peaks at A $\sim$ 130 and 195, we find that the NSMs can resolve the underproduction problems of such CCSN model prediction for the elements just below and above the abundance peaks. We discuss relative contribution to the solar-system r-process yields from CCSNe and NSMs. [Preview Abstract] |
Friday, October 10, 2014 10:30AM - 10:45AM |
FD.00007: Pasta Nucleosynthesis: Molecular dynamics simulations of nuclear statistical equilibrium Matthew Caplan, Charles Horowitz, Andre da Silva Schneider, Donald Berry We simulate the decompression of cold dense nuclear matter, near the nuclear saturation density, in order to study the role of nuclear pasta in r-process nucleosynthesis in neutron star mergers. Our simulations are performed using a classical molecular dynamics model with $51\,200$ and $409\,600$ nucleons, and are run on GPUs. We expand our simulation region to decompress systems from initial densities of 0.080 fm$^{-3}$ down to 0.00125 fm$^{-3}$. We study proton fractions of $Y_{P}=$ 0.05, 0.10, 0.20, 0.30, and 0.40 at $T=$ 0.5, 0.75, and 1 MeV. We calculate the composition of the resulting systems using a cluster algorithm. This composition is in good agreement with nuclear statistical equilibrium models for temperatures of 0.75 and 1 MeV. However, for proton fractions greater than $Y_{P}=$ 0.2 at a temperature of $T =$ 0.5 MeV, the MD simulations produce non-equilibrium results with large rod-like nuclei. Our MD model is valid at higher densities than simple nuclear statistical equilibrium models and may help determine the initial temperatures and proton fractions of matter ejected in mergers. [Preview Abstract] |
Friday, October 10, 2014 10:45AM - 11:00AM |
FD.00008: Constraining the equation of state of neutron stars from binary mergers Kentaro Takami, Luciano Rezzolla, Luca Baiotti Determining the equation of state of matter at nuclear density and hence the structure of neutron stars has been a riddle for decades. We show how the imminent detection of gravitational waves from merging neutron star binaries can be used to solve this riddle. Using a large number of numerical-relativity simulations of binaries with nuclear equations of state, we have found that the postmerger emission is characterized by two distinct and robust spectral features. While the high-frequency peak has already been associated with the oscillations of the hypermassive neutron star produced by the merger and depends on the equation of state, a new correlation emerges between the low-frequency peak, related to the merger process, and the compactness of the progenitor stars. More importantly, such a correlation is essentially universal, thus providing a powerful tool to set tight constraints on the equation of state. If the mass of the binary is known from the inspiral signal, the combined use of the two frequency peaks sets four simultaneous constraints to be satisfied. Ideally, even a single detection would be sufficient to select one equation of state over the others. We have tested our approach with simulated data and verified it works well for all the equations of state considered. [Preview Abstract] |
Friday, October 10, 2014 11:00AM - 11:15AM |
FD.00009: Cosmological Solutions to the Big-Bang Lithium Problem Toshitaka Kajino The 7Li abundance calculated in BBN with the baryon-to-photon ratio fixed from fits to the CMB power spectrum is inconsistent with the observed lithium abundances in metal-poor halo stars. Previous cosmological solutions proposed to resolve the problem include photon cooling (possibly via the Bose-Einstein condensation of a scalar particle), or the decay of a relic X-particle (possibly the next-to-lightest SUSY particle). In this talk we reanalyze these solutions both separately and in concert by taking account of a primordial magnetic field (PMF) that suggests many observable signatures in the CMB anisotropies. Especially, we precisely study the effects of atomic excitation of exotic X-nuclei and also its mass dependence on the BBN, and finally deduce the updated constraints on the initial abundance and lifetime of the X-particle \quad in the context of revised upper limits to the primordial 6Li abundance. We also suggest a new important reaction path to 9Be production. [Preview Abstract] |
Friday, October 10, 2014 11:15AM - 11:30AM |
FD.00010: Measurement of the proton production rate of the $^{23}$Na($\alpha$,p)$^{26}$Mg reaction relevant for Galactic $^{26}$Al S. Almaraz-Calderon, M. Albers, C.R. Hoffman, C.L. Jiang, K.E. Rehm, C. Ugalde, P.F. Bertone, M. Alcorta, C.M. Deibel, S.T. Marley The observation of $^{26}$Al in the galactic interstellar medium via its 1809-keV gamma ray confirmed that active nucleosynthesis takes place in the Galaxy. The $^{23}$Na($\alpha$,p)$^{26}$Mg reaction directly influences the production of $^{26}$Al in convective C/Ne burning shell of massive presupernova stars. We have performed a direct measurement of the $^{23}$Na($\alpha$,p)$^{26}$Mg reaction cross section at astrophysically important energies. The rate of proton production via this mechanism was found to be much higher than theoretical estimates. This change in the cross section will strongly affect the production of $^{26}$Al in massive stars and the contribution to proton production from the $^{23}$Na($\alpha$,p)$^{26}$Mg reaction should now be correctly incorporated into the astrophysical models. [Preview Abstract] |
Friday, October 10, 2014 11:30AM - 11:45AM |
FD.00011: Direct studies of ($\alpha$,p) reactions with HELIOS Jianping Lai, J.C. Blackmon, C.M. Deibel, D. DiMarco, H. Gardiner, A. Lauer, D. Santiago-Gonzalez, C. Williams, B. DiGiovine, J. Greene, J. Rohrer In a variety of astrophysical processes, ($\alpha$,p) type reactions have significant effects on final energy output and elemental abundances. However, only a handful of reactions have been measured due to technical limitations. Innovative new equipment and techniques, therefore, are necessary to extend measurement limits of these reactions rates. The HELIcal Orbit Spectrometer(HELIOS), serves as an important tool in studying reactions using radioactive ion beams at the Argonne Tandem Linac Accelerator System facility. With a specially designed gas target, we are able to study ($\alpha$,p) reaction directly. HELIOS can separate protons from reactions with different energy states and the heavy recoils can be detected in coincidence by a high efficiency gas ionization detector. This combination has been successful in our pilot experiments. A series of ($\alpha$,p) experiments using this setup in HELIOS are planned. We will start with $^{20}$Ne($\alpha$,p), which is crucial in Type Ia supernovae. A direct measurement of $^{30}$S($\alpha$,p), a key reaction in X ray burst, is also included in the near future plans and the beam development of $^{30}$S is in progress. Preliminary results will be presented. [Preview Abstract] |
Friday, October 10, 2014 11:45AM - 12:00PM |
FD.00012: Resonance strengths of the $^{34}$S + $\alpha$ reaction P.D. O'Malley, Devin Connolly, Uwe Greife, Ulrike Hager, Sergey Ilyushkin, Lothar Buchmann, Greg Christian, John D'Auria, Barry Davids, Jennifer Fallis, Dave Hutcheon, Lars Martin, Chris Ruiz, Alan Chen, Kiana Setoodehnia, Charles Akers, Brian Fulton, Alison Laird, Luke Erikson Late in their evolution, particularly massive stars undergo a stage of explosive oxygen burning. The free $\alpha $-particle density will rapidly increase and initiate a network of reactions among nuclides ranging from $^{28}$Si to $^{40}$Ca. Next there will be a abrupt rise in the abundances of $^{34}$S and $^{38}$Ar where the small excess of neutrons reside. The final abundances of nuclei in this mass region depend on the reaction cross sections involving these two nuclei. Currently there are large discrepancies in the strengths of the $^{34}$S$+\alpha $ resonances in the energy range of interest for this astrophysical environment. A new measurement was performed at DRAGON to resolve these discrepancies. Preliminary data will be shown and tentative results discussed. [Preview Abstract] |
Friday, October 10, 2014 12:00PM - 12:15PM |
FD.00013: Analysis of relationship between the center for Astrophysics and the surrounding objects Yongquan Han The gravitation of the celestial body is mainly determined by the radiation intensity and speed of rotation, the rotation of the celestial body makes the radiation bend, that's why gravitation engenders. Due to the randomness and uncertainty of the radiation, lead to the middle of the celestial body has the strongest radiation (the ray is most probably exist in the middle), one celestial body has only one angular velocity, so the position of the largest gravitation should be in the equatorial plane, so it is easy to draw: each independent surrounding objects are circling around the objects in the center for Astrophysics. When the Galaxy developing to a certain stage (Galaxy maturity), it should show as the shape of the solar system. Thus the expression of the gravitational field strength size is E$=$G(B$\times \rho \times T \times S \times \omega)$/R$^{2}$. R is the distance from the radiation source center. $\omega $ is the emitter's rotation angular velocity. G is the gravitational constant. B is the radiant intensity ratio constant. $\rho $ is the object density. T is the thermodynamic temperature. S is the surface area. [Preview Abstract] |
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