Christopher West, Alexander Heger, Sam M. Austin
We study the sensitivity of presupernova evolution and supernova nucleosynthesis yields of massive stars to variations of the helium-burning reaction rates within the range of their uncertainties. We use the current solar abundances from Lodders (2009) for the initial stellar composition. We compute a grid of 12 initial stellar masses and 176 models per stellar mass to explore the effects of independently varying the 12^C(a,g)16^O and 3a reaction rates, denoted R_a12 and R_3a, respectively. The production factors of both the intermediate-mass elements (A=16-40) and the s-only isotopes along the weak s-process path (70Ge, 76Se, 80Kr, 82Kr, 86Sr, and 87Sr) were found to be in reasonable agreement with predictions for variations of R_3a and R_a12 of +/-25%; the s-only isotopes, however, tend to favor higher values of R_3a than the intermediate-mass isotopes. The experimental uncertainty (one standard deviation) in R_3a(R_a12) is approximately +/-10%(+/-25%). The compactness parameter was used to assess which models would likely explode as successful supernovae, and hence contribute explosive nucleosynthesis yields. We also provide the carbon mass fraction at the end of core-helium burning as a key parameter for later evolution stages, and approximate remnant masses for each model.
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http://arxiv.org/abs/1212.5513
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