Collaborative Research: Empirical Constraints on the s- and r-processes from Precision Nebular Abundances

The origin of elements heavier than the iron-peak elements is an important question in modern astrophysics. The goal of this research project is to better define the relative contributions of the slow (s-) and rapid (r-) neutron(n)-capture processes, which occur respectively in dying Sun-like stars and in mergers of neutron stars, to the cosmic abundances of the trans-iron elements. To achieve that goal, the investigators will measure infrared and optical spectra of the ions of six n-capture elements (Se, Br, Rb, Te, Xe, and Kr) in a diverse sample of planetary nebulae (PNe) in the Milky Way and the Magellanic Clouds. Their analyses will reveal accurate abundances that reflect the amount of each element produced in the star before it became a planetary nebula. Results from the project will advance astronomers’ understanding of nucleosynthesis and galactic chemical evolution. This project will provide authentic research experiences to undergraduate students and support a vibrant program of science outreach to high school students. Using multiple ions of each element, the investigators will derive elemental abundances with far higher precision relative to previous determinations. The robust abundance determinations will yield reliable s-process elemental enrichment factors in Asymptotic Giant Branch (AGB) stars, which are the progenitors of PNe and major s-process sites in stellar populations. Quantifying the s-process contributions in PNe spanning a wide range in progenitor mass and metallicity will allow the investigators to place stringent empirical constraints on the range of r-process contributions to these elements and their candidate sites. It will also allow them to distinguish between different sets of evolutionary and nucleosynthetic models for AGB stars. 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.