Speaker
Description
Planetary nebulae (PNe), the descendants of AGB stars, are characterized by carbon, nitrogen,
and neutron(n)-capture element (atomic number Z > 30) enrichments that result from AGB
nucleosynthesis. In particular, n-capture elements can be formed via the s-process during the
thermally-pulsing AGB, and their abundances hold clues to poorly-understood processes in AGB
stars including the treatment of convection, mass loss, and mixing across convective
boundaries. Measuring the amount of freshly synthesized n-capture elements emerging from
AGB stars constitutes critical input for modeling galactic chemical evolution. Many of the
elements observed in PNe (e.g., Se, Kr, Te, and Xe) cannot be detected in AGB stars. These
species lie on or near r-process peaks, and nebular abundances provide key information
regarding how the s-process contributes to their production in the Universe. In this talk I will
discuss results of recent and ongoing investigations that aim to determine accurate and precise
abundances of n-capture elements in PNe. Our group has conducted multi-wavelength
spectroscopic observations of Galactic and Magellanic Cloud PNe that have detected multiple
ionization states of n-capture elements. This reduces uncertainties in correcting for unobserved
ions, enabling the determination of accurate elemental abundances and enrichment factors from
observations that do not include lines of all relevant ions of a given element. These studies
place new constraints on s-process nucleosynthesis in stars with metallicities 10% solar up to
solar, and indirectly on r-process enrichments in the present-day Universe.