Collaborative Research: RUI: Understanding Stellar Structure Using Lithium and New Steps Toward the Big Bang Lithium Abundance

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The abundance of Lithium, relative to Hydrogen, is a key prediction of Big Bang models of the early universe. Abundances of the elements can be measured using the absorption lines in stellar spectra. But Lithium can also be destroyed in stars when convection mixes surface material with the hotter stellar interiors. Low abundance of Lithium in stellar atmospheres is seen among stars where processes that deplete Lithium would not be expected to occur, and abundances are far lower than predicted for stars where such depletion processes are expected to be operating. This team will measure the abundance of Lithium in the atmospheres of a carefully selected sample of stars in order to better understand physical processes inside stars. They hope to determine whether the Sun is a normal or abnormal star for its mass and age, whether there is variation in Lithium destruction among supposedly identical stars, and better understand the disagreement between the Big Bang Lithium abundance inferred from the microwave background observations and that seen in stellar atmospheres. This is a collaborative effort among astronomers at four universities, including a predominantly undergraduate institution. This project will lead to at least one PhD thesis and extend the educational opportunities for undergraduates at the individual schools by integrating a team of students in a large-scale research program, using astronomical observatories in Arizona, California, and Australia.The research team will extend and expand its spectroscopic studies of stars in open and globular clusters, emphasizing the old open clusters M67 and NGC188, and the nearest globular cluster, NGC6397. Their goals are (a) determine whether the Sun is a normal or abnormal star for its mass and age, (b) determine if there is variation in the physical mechanisms controlling Li destruction among supposedly identical stars, (c) pioneer studies on the role of stellar metal content in determining the level of Li-depletion, and (d) study the potential impact of stellar evolution on metal deficient stars of the halo, with implications for the true level of disagreement (if any) between the value of the Big Bang Li abundance inferred from the microwave background versus that inferred from halo dwarf surface Li abundances.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.