Exploring the Nucleosynthesis of Neutron-Capture Elements Through Nebular Spectroscopy

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Dr. Nicholas Sterling is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at Michigan State University. Dr. Sterling will conduct a spectroscopic investigation of planetary nebulae (PNe) and Wolf-Rayet (WR) nebulae, in order to investigate the production of neutron(n)-capture elements (atomic number Z 30) by s-process nucleosynthesis in the progenitor stars of these objects. He will observe PNe with a wide range of progenitor masses in the optical spectral region, which provides access to several n-capture elements that are not detectable in stellar spectra. These data will be used to derive s-process enrichment factors, determine key physical conditions and constrain the element-by-element pattern of s-process enrichments in PN progenitor stars with different initial masses, and reveal the s-process neutron source in intermediate-mass AGB stars. In addition, Dr. Sterling will observe WR nebulae in the infrared in order to detect emission lines of Se and Kr, two of the most highly enriched elements by the weak s-process. This will potentially provide some of the first observational evidence of weak s-process enrichments in massive stars. These observations will be complemented by a laboratory astrophysics study to determine atomic data needed to accurately derive the abundances of the n-capture elements Br and Rb in ionized nebulae. The atomic data will be added to the atomic databases of state-of-the-art photoionization codes and made accessible to the broad astrophysical community. This research has implications for the origin and chemical evolution of trans-iron elements in the Universe, and nucleosynthesis and convective mixing during the late stages of stellar evolution. Moreover, this work will establish an observational and atomic physics foundation upon which future nebular studies can be built, enabling chemical evolution investigations of these elements in Galactic and extragalactic environs.Dr. Sterling will also manage an educational outreach program at Michigan State University comprised of designing and teaching seminars for students, co-teaching Physics and Astronomy Department courses, and advising an undergraduate student research project. The content of the seminars, which will be offered at a range of levels, will draw from the research activities of Dr. Sterling and make them accessible to university students.