Bulletin of the American Physical Society
81st Annual Meeting of the APS Southeastern Section
Volume 59, Number 18
Wednesday–Saturday, November 12–15, 2014; Columbia, South Carolina
Session BC: Astrophysics |
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Chair: Richard Longland, North Carolina State University Room: Richland II |
Thursday, November 13, 2014 8:30AM - 9:06AM |
BC.00001: Nuclear physics challenges and opportunities for nova nucleosynthesis Invited Speaker: D.W. Bardayan Nuclear physics determines the properties of a variety of astrophysics events from the relatively constant and unchanging night sky to the cataclysmic explosions that enrich the Cosmos with their ashes. Owing to their relatively high frequency ($\sim$ 25 in our Galaxy per year), novae provide a prime opportunity to study nucleosynthesis under extreme conditions. This nucleosynthesis is largely determined by the properties and reactions on proton-rich radioactive nuclei from roughly carbon to calcium. In fact, novae are probably the only explosive astrophysics events for which there is a reasonable opportunity to study all of the reactions of interest within our lifetimes. This talk will explore the nuclear physics needs and challenges that must be met in order to accurately model nova nucleosynthesis with a focus on those nuclear reactions that strongly impact observables upon which we benchmark nova models. Emerging frontiers and opportunities for experimental advances will also be presented. [Preview Abstract] |
Thursday, November 13, 2014 9:06AM - 9:42AM |
BC.00002: Multi-dimensional Simulations of Mixing in Classical Novae Invited Speaker: Jordi Casanova Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass, main sequence star onto a white dwarf. The material piles up under degenerate conditions until a thermonuclear runaway ensues. The energy released by the suite of nuclear processes operating at the envelope heats the material up to peak temperatures about (0.1-0.4) GK. During these events, material enriched in CNO and other intermediate-mass elements, are ejected into the interstellar medium. To account for the gross observational properties of classical novae (in particular, a metallicity enhancement in the ejecta above solar values), numerical models assume mixing between the (solar-like) material transferred from the companion and the outermost layers (CO- or ONe-rich) of the underlying white dwarf. The origin of the large enhancements and inhomogeneous distribution of chemical species observed in high-resolution spectra of ejected nova shells has, however, remained unexplained for almost half a century. Here we investigate, with multi-D simulations, the role of Kelvin-Helmholtz instabilities as a natural mechanism for self-enrichment of the accreted envelope with core material. Such mixing also naturally produces large-scale chemical inhomogeneities. Both the metallicity enhancement and the intrinsic dispersions in the abundances are consistent with the observed values. [Preview Abstract] |
Thursday, November 13, 2014 9:42AM - 10:18AM |
BC.00003: Nucleosynthesis of $^{26}$Al in Classical Novae: Past, Present and Future Invited Speaker: Catherine Deibel The ground state of the unstable nucleus $^{26}$Al ($t_{1/2}=7.2\times 10^5$ yr) decays through the first excited state of $^{26}$Mg $99.7\%$ of the time resulting in the emission of a 1.809-MeV $\gamma$ ray. The distribution of this $\gamma$-ray line, first observed in 1979 [1], has been measured along the Galactic plane by several balloon-borne and satellite experiments, confirming the on-going nucleosynthesis of $^{26}$Al in the Galaxy. The stellar source of this isotope has been the subject of debate, but current estimates indicate the majority is produced in massive stars, while $20-30\%$ is synthesized in classical ONe novae. The situation is further complicated by the existence of an isomeric state at 228 keV ($^{26}$Al$^m$: $J^{\pi}=0^+$, $t_{1/2}=6.3$ s), which $\beta$ decays directly to the ground state of $^{26}$Mg, bypassing the emission of the 1.809-MeV $\gamma$ ray. There are three reaction sequences that produce $^{26}$Al$^{g,m}$ in classical novae, and a variety of studies have been performed to determine the rates of the various reactions involved (e.g. [2-4]). A survey of these measurements will be given, as well as the current status of $^{26}$Al production in novae. Future plans to accurately determine the reaction rates that dominate the remaining uncertainties in $^{26}$Al nucleosynthesis will also be discussed. \\[4pt] [1] W. A. Mahoney $et$ $al.$, Astrophys. J. {\bf 286}, 578 (1984).\\[0pt] [2] C. M. Deibel $et$ $al.$, Phys. Rev. C {\bf 80}, 035806 (2009).\\[0pt] [3] G. Lotay $et$ $al.$, Phys. Rev. C {\bf 80}, 055802 (2009).\\[0pt] [4] M. B. Bennett $et$ $al.$, Phys. Rev. Lett. {\bf 111}, 232503 (2013). [Preview Abstract] |
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