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T. P. Swift (Case Western University), B. S. Meyer, L.-S. The (Clemson University)
The origin of the light, neutron-capture bypassed (p-process) isotopes 92Mo, 94Mo, 96Ru, and 98Ru has long been a mystery. Sites that produce the majority of the p-process isotopes in correct solar proportions have long been known to underproduce the light species [1], thereby suggesting a different origin. The alpha-rich freezeout occurring near a nascent neutron star in Type II supernovae has been proposed [2,3,4]; however, only 92Mo is strongly produced, and it is never the most overproduced isotope, as is required for its site of origin. We explore models of alpha-rich freezeouts that include simultaneous irradiation of the nuclei by the copious neutrinos emitted during the explosion. We find that neutrino-nucleus interactions significantly enhance production of the light p-process species both by affecting the electron-nucleon ratio during the nucleosynthesis and by increasing the charge of nuclei once nuclear quasi-equilibrium clusters have broken. In many models studied, the light p-process isotopes are the most overproduced species, which supports the idea of this being a possible production site. The neutrino fluences required for light p-process isotope production are high--probably somewhat higher than current supernova models allow. Nevertheless, the results are encouraging and suggest further work is needed on this promising site.
This work was supported by the NSF Research Experiences for Undergraduates (REU) Site Program through grant AST 96169939 to Florida Tech and the Southeastern Association for Research in Astronomy (SARA). It was also supported by NSF grant AST 9819877 and NASA grant NAG5-4703 at Clemson University.
References:
[1] Woosley, S. E., and Howard, W. M. 1978, ApJS, 36, 285
[2] Woosley, S. E., and Hoffman, R. D. 1992, ApJ, 395, 202
[3] Fuller, G. M., and Meyer, B. S. 1995, ApJ, 453, 792
[4] Hoffman, R. D., Woosley, S. E., Fuller, G. M., and Meyer, B. S. 1996, ApJ, 460, 478