Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session L5: Nuclear Physics in Astrophysics: From Stars to Stellar Explosions |
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Sponsoring Units: DNP DAP Chair: Sam Austin, Michigan State University Room: Governor's Square 15 |
Sunday, May 3, 2009 3:30PM - 4:06PM |
L5.00001: Hans A. Bethe Prize Talk: The Physics of Stars Invited Speaker: John von Neumann speculated that computers might become sufficiently powerful that they could be used to solve analytically intractable problems numerically (he gave turbulence as an example), and that those ``numerical experiments" could be used to provide the insight necessary to develop analytic solutions. A case study will be presented in which we attempt in this way to use computer simulations of 3D turbulent flow in presupernova stars. We find that we can reproduce the simulations surprisingly well---on average---if we replace the viscous term with an effective damping which turns out to be similar to that inferred by Kolmogorov for a turbulent cascade. Stars are gravitationally-controlled thermonuclear reactors. Abundance change (and hence evolution) occurs because of nuclear burning, and mixing. It is now possible to treat this coupled problem in a self-consistent way, free of astronomically calibrated parameters. Implications for stellar evolution, nucleosynthesis yields, core collapse, supernova explosions, helio-seismology, and solar neutrinos will be discussed. It is argued that advances in the treatment of stellar fluid dynamics, along with new developments in laboratory astrophysics, now allow far more reliable predictions of how stars behave. [Preview Abstract] |
Sunday, May 3, 2009 4:06PM - 4:42PM |
L5.00002: Dimming Metals: the Effect of Progenitor Metallicity on the 56Ni Yield and Luminosity of Type La Supernovae Invited Speaker: |
Sunday, May 3, 2009 4:42PM - 5:18PM |
L5.00003: Test of Weak Reaction Rates of Importance for Late Stellar Evolution Using Charge-exchange Reactions. Invited Speaker: Weak reactions (electron captures and beta decays) on nuclei play an important role in the evolution of pre-supernovae stars and their eventual core collapse. The rates are usually predicted in shell-model and mean-field calculations. Experimental information on Gamow-Teller strength distributions is needed to test these calculations. At the NSCL, the (t,$^{3}$He) charge-exchange reaction at 115 MeV/nucleon is employed for such studies. In addition, the ($^{3}$He,t) reaction at 140 MeV/nucleon (at RCNP, Osaka) is used for detailed studies of the charge-exchange reaction mechanism, which is important for understanding the uncertainties in the experimentally extracted Gamow-Teller strength distributions. Besides a comparison between experimental and theoretical Gamow-Teller strength distributions, the work also includes the calculation of electron-capture rates, so that the sensitivity of the rates on differences between theoretical and experimental rates can be gauged. A significant fraction of the nuclei relevant for late stellar evolution are unstable. Hence, to ensure accurate weak reaction rates for such nuclei, charge-exchange experiments on rare isotopes are crucial, but the techniques have to be developed. At the NSCL, a program has been initiated to study charge-exchange reactions on rare isotopes. [Preview Abstract] |
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