Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session BA: Recent Progress in Nuclear Astrophysics |
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Sponsoring Units: DNP JPS Chair: G. Fuller, University of California, San Diego Room: Ritz-Carlton Hotel Salon 4 |
Monday, September 19, 2005 7:00PM - 7:45PM |
BA.00001: Damped Lyman Alpha Systems: Neutral gas Reservoirs for Star Formation and Element Production at High Redshifts Invited Speaker: Damped Lya systems (DLAs) are a population of quasar absorption systems that dominate the neutral-gas content of the Universe in the redshift interval $z$=[0,5]. I discuss evidence that the DLAs serve as important neutral-gas reservoirs for star formation at high redshifts, and as a result, appear to be the progenitors of modern galaxies. Specifically, accurate measurements of the neutral-gas mass per unit comoving volume, $\Omega_{gas}$, reveals evidence for a statistically significant decrease in $\Omega_{gas}$ with time, which is suggestive of gas consumption by star formation. Further indirect evidence for star formation stems from the observed increase in metal abundance with time, which indicates element enrichment by star formation: measurements of abundance ratios such as (Si/Fe) and of the ``odd-even'' effect further indicate metal enrichment primarily by type II supernovae. Finally, I discuss a technique for measuring the heating rate of the gas. The most plausible heat source is shown to be UV radiation emitted by massive stars residing in DLAs. The implied UV luminosity per unit comoving volume implies that a subset of DLAs is heated by compact regions of intense star formation that are identified as the Lyman break galaxies. [Preview Abstract] |
Monday, September 19, 2005 7:45PM - 8:30PM |
BA.00002: Experimental studies of high-temperature hydrogen burning using low-energy radioactive beams Invited Speaker: Nuclear reactions of unstable nuclei play a key role in explosive burning in the universe. We have been conducting experiments with low-energy radioactive beams to learn the critical nuclear reactions under explosive condition, especially the early stage of the rp- process. We will report recent results using the CRIB separator at CNS, University of Tokyo. Low-energy radioactive beams at about 5 MeV/nucleon or below are produced by the low-energy in-flight method from high-intensity heavy-ion primary beams. The CRIB line, consisting of a magnetic separator and a Wien filter, can effectively purify the secondary beams. A series of experiments was performed to study proton elastic resonance scattering (A+p) with unstable nucleus A. The information of the A+p resonances ($E_x$, $J^\pi$ and $\Gamma$) in nucleus B may help understand resonance contributions to hydrogen-burning A (p,$\gamma$)B reactions under high temperature conditions. We will show the resonance data of $^{11}$C+p/$^{12}$N+p (relevant to the hot pp-chain), $^{13}$N+p (hot CNO), $^{23}$Mg+p (break out from the NeNa cycle), and some others. Other experimental projects for measurements of stellar reactions are in progress. For example, the direct measurement of $^{14}$O($\alpha$,p)$^{17}$F at the first stage of the high-temperature rp-process was performed for the first time using a high-intensity $^{14}$O beam and a thick cold He target. The current status of the projects and future outlook will be discussed. [Preview Abstract] |
Monday, September 19, 2005 8:30PM - 9:15PM |
BA.00003: Neutrinos and the r-process Invited Speaker: While the mechanism for producing the heaviest elements has been understood for half a century, the astrophysical site remains a mystery. We will consider and compare two possible sites - the neutrino driven wind of the type II supernovae and the outflow from accretion disks surrounding black holes. These disks are likely to form from either neutron star mergers or from the collapse of rapidly rotating massive stars. In either case there is a significant flux of neutrinos which will impact the neutron-to-proton ratio and thus the nucleosynthesis. We will discuss the role of the neutrinos and the prospects for obtaining an r-process in each environment. [Preview Abstract] |
Monday, September 19, 2005 9:15PM - 10:00PM |
BA.00004: Core-collapse supernovae, r-process nucleosynthesis, and the physics of unstable nuclei Invited Speaker: Recent findings of r-process elements in extremely metal- poor stars are considered to be clear evidence that these heavy elements are created in explosive astrophysical phenomena such as core-collapse supernovae. Accumulated observational data suggest further that there might be more than one episode responsible for the r-process nucleosynthesis. These observed facts are the important clues to identify the astrophysical origin of r-process elements, and furthermore strengthen the motivation to clarify the explosion mechanism of core-collapse supernovae.\\ I discuss two aspects of supernova physics in this invited talk:\\ First, I discuss that the r-process depends on the outcome of supernova explosions from various progenitor masses through hydrodynamical mass ejection mechanism, thermodynamic conditions of the neutrino-driven winds, and others. We demonstrate that the nuclear reactions of neutron-rich nuclei in the light mass region play the crucial roles in the r-process. \\ Secondly, I discuss recent progress and continuing efforts in understanding explosion mechanism of core-collapse supernovae, in the light of nuclear physics of unstable nuclei. The data table of relativistic equation of state (EOS), which we have constructed by adopting the data of unstable nuclei such as neutron-skin thickness, enables us to study the influence of EOS in modern supernova simulations. I report on how the supernova dynamics is different each other with the new EOS table and the conventional set of EOS. I also reveal the thermal evolution of central core at late stage and the resulting signals of supernova neutrinos. I stress that the different compositions including neutron-rich nuclei would appear in supernova cores, so that they might change the electron-capture and neutrino- reaction rates to help successful explosions. I discuss current needs and possible extensions of nuclear physics in supernova simulations. [Preview Abstract] |
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