The following are our recent preprints. If you are looking for a paper and do not find it here, please check our publications page.
Nucleosynthesis and Chemical Evolution of Oxygen
Authors: Bradley S. Meyer, Larry R. Nittler, Ann N. Nguyen, Scott Messenger
Abstract: Of the elements strictly synthesized in stars, oxygen is by far the most abundantly produced. We review the nucleosynthesis and Galactic chemical evolution of this important element. We then review its isotopic composition in presolar grains recovered from primitive meteorites and from interplanetary dust particles. As we describe, knowledge of these isotopic compositions provide important constraints on theories of nucleosynthesis, stellar evolution, and Galactic chemical evolution.
Preprint: pdf (submitted to Reviews in Mineralogy and Geochemistry in 2008)
s-process Nucleosynthesis in Advanced Burning Phases of Massive Stars
Authors: Lih-Sin The, Mounib F. El Eid, Bradley S. Meyer
Abstract: We present a detailed study of s-process nucleosynthesis in massive stars of solar-like initial composition and masses 15, 20, 25, and 30 solarmass. We update our previous results of s-process nucleosynthesis during the core He-burning of these stars and then focus on an analysis of the s-process under the physical conditions encountered during shell-carbon burning. We show that the recent compilation of the 22Ne(alpha,n)25Mg rate leads to a remarkable reduction of the efficiency of the s-process during core He-burning. In particular, this rate leads to the lowest overproduction factor of 80Kr found to date during core He-burning in massive stars. The s-process yields resulting from shell carbon burning turn out to be very sensitive to the structural evolution of the carbon shell. This structure is influenced by the mass fraction of 12C attained at the end of core helium burning, which in turn is mainly determined by the 12C(alpha,gamma)16O reaction. The still present uncertainty in the rate for this reaction implies that the s-process in massive stars is also subject to this uncertainty. We identify some isotopes like 70Zn and 87Rb, which are indicators of the s-process during shell carbon burning in massive stars.
Preprint: pdf (submitted to Astrophysical Journal in 2005)
Free-Nucleon/Alpha-Particle Disequilibrium and r-Process Nucleosynthesis
Authors: Bradley S. Meyer, Changyuan Wang
Abstract: We demonstrate that if r-process nucleosynthesis occurs in expansions of matter from high temperature and density in which free nucleons are persistently in disequilibrium with alpha particles, then the resulting abundance distribution can be highly sensitive to the magnitude of strong and electromagnetic reaction cross sections on heavy nuclei. For the particular expansions studied in this work, reactions on nuclei in the atomic number range Z ≈ 40 and Z ≈ 55 have the largest effect. These nuclei may be important targets for near-term nuclear cross section experiments.
Preprint: pdf (submitted to Proceedings 3rd RIA Workshop/Argonne in 2006)
