The chemical composition of stars holds the answers for many of the most fundamental questions about our universe. In particular, the study of the light elements, lithium, beryllium, and boron, is important in many areas of modern astrophysics, such as Big Bang nucleosynthesis, the origin of the elements, Galactic chemical evolution, stellar interiors and evolution.
Here, three projects will be carried out. The first is the determination of beryllium abundances in the oldest stars with metal contents lower than one one-thousandth that of the sun. If a "plateau" in beryllium abundances is found among such stars, it will imply an inhomogeneity in the early universe with high-density proton-rich bubbles. The second project is a study of the chemical evolution of the Galaxy through the growth in the beryllium content over time. The enrichment of various chemical elements in the Galaxy reveals the history of formation of massive stars and the early production of supernovae. Tracking the increase of beryllium over time gives sensitive information about previous generations of stars. Probing both the earliest times (via observations of stars with low metal contents) and the intermediate ages will result in a greater understanding of the evolution of the Galaxy. Finally, most stars of low metallicity have a similar lithium content due to the production of lithium during the Big Bang. However, some of these very old stars are deficient in lithium. In the third project, by determining the beryllium content in the lithium-deficient old stars, two competing theories of the origin of the lithium depletions will be tested (mixing, which should destroy lithium but not beryllium, and mass transfer, which should deplete both elements). Understanding this will illuminate stellar mixing processes and the primordial lithium value.
This research will take advantage of two of the world's largest telescopes: the Keck-I 10-m telescope and the Subaru 8.2-m telescope at the Manna Kea Observatory. Graduate students will be supported and trained to use these telescopes and conduct research in the compositions of stars.
