We explore the variation in single star 15-30 M , non-rotating, solar metallicity, pre-supernova MESA models due to changes in the number of isotopes in a fully-coupled nuclear reaction network and adjustments in the mass resolution. Within this two-dimensional plane we quantitatively detail the range of core masses at various stages of evolution, mass locations of the main nuclear burning shells, electron fraction profiles, mass fraction profiles, burning lifetimes, stellar lifetimes, and compactness parameter at core-collapse for models with and without mass loss. Up to carbon burning we generally find mass resolution has a larger impact on the variations than the number of isotopes, while the number of isotopes plays a more significant role in determining the span of the variations for neon, oxygen and silicon burning. Choice of mass resolution dominates the variations in the structure of the intermediate convection zone and secondary convection zone during core and shell hydrogen burning respectively, where we find a minimum mass resolution of ≈0.01 M is necessary to achieve convergence in the helium core mass at the ≈5% level. On the other hand, at the onset of core-collapse we find ≈30% variations in the central electron fraction and mass locations of the main nuclear burning shells, a minimum of ≈127 isotopes is needed to attain convergence of these values at the ≈10% level.

We discuss the possibility whether superheavy elements can be produced in Nature by the astrophysical rapid neutron capture process. To this end we have performed fully dynamical network r-process calculations assuming an environment with neutron-to-seed ratio large enough to produce superheavy nuclei. Our calculations include two sets of nuclear masses and fission barriers and include all possible fission channels and the associated fission yield distributions. Our calculations produce superheavy nuclei with A ≈ 300 that however decay on timescales of days.PACS. 26.30.Hj r-process -27.90.+b Properties nuclei with A ≥ 220 -25.85.-w Fission reactions arXiv:1207.3432v1 [nucl-th]

We investigate properties of carbon-oxygen white dwarfs with respect to the composite uncertainties in the reaction rates using the stellar evolution toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the probability density functions in the reaction rate library STARLIB. These are the first Monte Carlo stellar evolution studies that use complete stellar models. Focusing on 3 M models evolved from the pre main-sequence to the first thermal pulse, we survey the remnant core mass, composition, and structure properties as a function of 26 STARLIB reaction rates covering hydrogen and helium burning using a Principal Component Analysis and Spearman Rank-Order Correlation. Relative to the arithmetic mean value, we find the width of the 95% confidence interval to be ∆M 1TP ≈ 0.019 M for the core mass at the first thermal pulse, ∆t 1TP ≈ 12.50 Myr for the age, ∆ log(T c /K) ≈ 0.013 for the central temperature, ∆ log(ρ c /g cm −3 ) ≈ 0.060 for the central density, ∆Y e,c ≈ 2.6×10 −5 for the central electron fraction, ∆X c ( 22 Ne) ≈ 5.8×10 −4 , ∆X c ( 12 C) ≈ 0.392, and ∆X c ( 16 O) ≈ 0.392. Uncertainties in the experimental 12 C(α, γ) 16 O, triple-α, and 14 N(p, γ) 15 O reaction rates dominate these variations. We also consider a grid of 1 to 6 M models evolved from the pre main-sequence to the final white dwarf to probe the sensitivity of the initial-final mass relation to experimental uncertainties in the hydrogen and helium reaction rates.

We explore properties of core-collapse supernova progenitors with respect to the composite uncertainties in the thermonuclear reaction rates by coupling the reaction rate probability density functions provided by the STARLIB reaction rate library with MESA stellar models. We evolve 1000 15 M models from the pre main-sequence to core O-depletion at solar and subsolar metallicities for a total of 2000 Monte Carlo stellar models. For each stellar model, we independently and simultaneously sample 665 thermonuclear reaction rates and use them in a MESA in situ reaction network that follows 127 isotopes from 1 H to 64 Zn. With this framework we survey the core mass, burning lifetime, composition, and structural properties at five different evolutionary epochs. At each epoch we measure the probability distribution function of the variations of each property and calculate Spearman Rank-Order Correlation coefficients for each sampled reaction rate to identify which reaction rate has the largest impact on the variations on each property. We find that uncertainties in 14 N(p, γ) 15 O, triple-α, 12 C(α, γ) 16 O, 12 C( 12 C,p) 23 Na, 12 C( 16 O,p) 27 Al, 16 O( 16 O,n) 31 S, 16 O( 16 O,p) 31 P, and 16 O( 16 O,α) 28 Si reaction rates dominate the variations of the properties surveyed. We find that variations induced by uncertainties in nuclear reaction rates grow with each passing phase of evolution, and at core H-, He-depletion are of comparable magnitude to the variations induced by choices of mass resolution and network resolution. However, at core C-, Ne-, and O-depletion, the reaction rate uncertainties can dominate the variation causing uncertainty in various properties of the stellar model in the evolution towards iron core-collapse.