Enrichments of Trans-Iron Elements in Planetary Nebulae: Probing Stellar Evolution and Nucleosynthesis

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The atoms in our bodies, apart from hydrogen, were produced by nuclear reactions deep within stars that lived and died before our Solar System was born. The investigators will study the production of these chemical elements by stars like our Sun. When our Sun reaches an age of about 10 billion years, it will expand to become a red giant star. Such red giant stars later throw off material and form expanding, glowing clouds called planetary nebulae. Astronomers observe the light coming from these nebulae to study their chemical properties. The new, star-made elements flow into space and spread throughout our Milky Way Galaxy.This project lies at the crossroads of several scientific disciplines and motivates students over a range of educational levels to enter STEM fields, which addresses an important national need. The question "Where did the elements come from?" has broad appeal. The project will support a graduate student at the University of Texas (UT) and undergraduates at both UT and the University of West Georgia, which have substantial populations of underrepresented minorities (Hispanic and African-American respectively). Through teacher workshops the investigators will reach large numbers of high school students. Pure astronomical research has strong connections to other areas of physics. For example, some of the investigators' newly detected emission lines (e.g., rubidium, cadmium, and tellurium) were found at different energies than predicted, improving our understanding of atoms found on the Earth. The investigators' primary research method is near infrared and optical spectroscopy at high spectral resolution (R 40,000) to optimize detection of weak emission lines and avoid blends with other elements. They use standard procedures of nebular abundance analysis to derive ionic and elemental abundances from line flux measurements but incorporate new atomic models. The goals are to distinguish which evolutionary models are most realistic and to empirically establish the contributions of 1-8 solar mass stars to Galactic chemical evolution. The chemical yield of this numerous class of stars is a key ingredient for galactic archeology and inferring the star-forming history of the Milky Way Galaxy.