Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session Y3: Invited Session: R-Process Nucleosynthesis |
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Sponsoring Units: DNP DAP Chair: Charles Horowitz, Indiana University Room: Chatham Ballroom B |
Tuesday, April 8, 2014 1:30PM - 2:06PM |
Y3.00001: Kilonovae: Electromagnetic Counterparts of Neutron Star Mergers Powered by the Radioactive Decay of R-Process Nuclei Invited Speaker: Brian Metzger The coalescence of binary neutron stars (NSs) are the most promising sources for the direct detection of gravitational waves by Advanced LIGO and Virgo. However, maximizing the scientific opportunities from such a discovery will require the detection of a coincident electromagnetic counterpart. One possible counterpart is a short gamma-ray burst (GRB), powered by the accretion of NS debris left over from the merger onto the newly-formed black hole. However, GRBs are thought to be relativistically beamed and hence to accompany only a small fraction of mergers. NS mergers also produce isotropic supernova-like emission, powered by the radioactive decay of heavy (r-process) elements which are synthesized in the neutron-rich ejecta from the merger. I will describe the first calculations of such ``kilonovae'' which include realistic nuclear physics and radiative transport. In addition to providing a smoking gun for detecting binary NS mergers, kilonovae inform the unknown origin of the heaviest elements in the Universe. The first kilonova may have been discovered by the Hubble Space Telescope last year. [Preview Abstract] |
Tuesday, April 8, 2014 2:06PM - 2:42PM |
Y3.00002: Rare Isotopes Heating and Cooling the Crust of Accreting Neutron Stars Invited Speaker: Hendrik Schatz Observations of accreting neutron stars in X-ray binaries provide a unique window into the structure of neutron stars and the properties of dense matter. Observables such as thermonuclear bursts and cooling behavior are strongly affected by nuclear processes in the crust that involve neutron captures and beta decays on extremely neutron rich rare isotopes. These nuclear processes control nuclear heating, neutrino cooling, and compositional changes that affect thermal transport and need to be understood to interpret X-ray observations. The challenges for nuclear physics are similar to understanding the extremely neutron rich nuclei in the r-process. I will discuss recent progress in delineating the nuclear processes in accreting neutron stars, including a novel neutrino cooling process based on electron-capture and beta decay Urca cycles on nuclei in the outer crust. I will also discuss attempts to address the nuclear physics questions through laboratory measurements at rare isotope facilities and the prospects of obtaining most of the nuclear data in the near future with the new FRIB accelerator facility. [Preview Abstract] |
Tuesday, April 8, 2014 2:42PM - 3:18PM |
Y3.00003: Hans A. Bethe Prize: Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis Invited Speaker: Karl-Ludwig Kratz Guided by the Solar System (S.S.) abundance peaks at A$\simeq$130 and A$\simeq$195, the basic mechanisms for the rapid neutron-capture process (the {\it r-process}) have been known for over 50 years. However, even today, all proposed scenarios and sites face problems with astrophysical conditions as well as with the necessary nuclear-physics input. In my talk, I will describe efforts in experimental and theoretical nuclear-structure data for modeling today's three groups of r-process {\it ``observables''}, i.e. the bulk S.S. isotopic abundances, the elemental abundances in metal-poor halo stars, and peculiar isotopic patterns measured in certain cosmic stardust grains. To set a historical basis, I will briefly recall our site-independent {\it ``waiting-point''} model, with superpositions of neutron-density components and the use of the first global, unified nuclear input based on the mass model FRDM(1992). This approach provided a considerable leap forward in the basic understanding of the required astrophysical conditions, as well as of specific shell-structure properties far from stability. Starting in the early millenium, the above simple model has been replaced by more realistic, dynamical parameter studies within the high-entropy wind scenario of core-collapse supernovae, now with superpositions of entropy (S) and electron-fraction (Y$_e$) components. Furthermore, an improved, global set of nuclear-physics data is used today, based on the new mass model FRDM(2012). With this nuclear and astrophysics parameter combination, a new fit to the S.S. r-abundances will be shown, and its improvements and remaining deficiencies in terms of underlying shell structure will be discussed. Concerning the abundance patterns in metal-poor halo stars, an interpretation of the production of {\it ``r-rich''} (e.g. CS 22892-052) and {\it ``r-poor''} (e.g. HD 122563) stars in terms of different (Y$_e$), S combinations will be presented. Finally, for the third group of {\it ``r-observables''}, a possible origin of the anomalous Xe-H pattern in presolar nanodiamonds by the {\it ``main''} component of a {\it ``cold''} r-process is suggested. [Preview Abstract] |
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