Physics Colloquium with Nan Liu on Presolar Stardust

Nan Liu (Hosted by Gillis-Davis) from Washington University in St. Louis will be presenting the colloquium "Cosmic Forensics Using Presolar Stardust"

The chemical makeup of our solar system is a reflection of Galactic chemical evolution in the local interstellar medium (ISM) over the past ~9 Ga. Although the incorporated ISM dust was mostly destroyed during solar system formation, a small fraction of the ISM dust, known as presolar dust, is preserved in pristine extraterrestrial materials and identified through their exotic isotopic compositions, pointing to their formation in gas outflows or explosions of ancient stars. Since their stellar birth at more than 4.6 Ga, presolar grains have borne witness to a diverse array of astrophysical and cosmochemical processes. In particular, presolar grain analysis has rapidly become an important component of nuclear astrophysics, as it allows for isotope analysis of bona fide stellar material in the laboratory at a precision that far exceeds what can be achieved by spectrographic measurements using state-of-the-art telescopes.

In this talk, Liu will outline how we can utilize the isotopic and structural compositions of presolar grains to constrain physical mixing processes in stars, stellar nucleosynthesis, dust formation, and the origin and evolution of the solar system. First, she will discuss the unique role of presolar grains derived from asymptotic giant branch (AGB) stars in constraining the slow neutron-capture process (s-process), which is ultimately responsible for producing half of the heavy elements beyond iron in the solar system. She will focus on bottleneck isotopes along the s-process path and discuss how their abundances in presolar grains can be harnessed to constrain the physical processes responsible for engendering the major neutron source for the s-process in AGB stars. Second, Liu will describe how to employ radioactive isotope abundances and structural compositions of presolar grains originated from core-collapse Type II supernovae to constrain dust formation and timing, as well as the physicochemical conditions after the explosions and the deep links to astronomical observations. Throughout the presentation, she will simultaneously lay out her future research plans to probe the intermediate neutron-capture process, supernova remnants, and solar system evolution by performing cutting-edge analyses of presolar grains in primitive meteorites and samples returned from missions.

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