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Paper: An Infrared Survey of Neutron-Capture Elements in Planetary Nebulae
Volume: 336, COSMIC ABUNDANCES as Records of Stellar Evolution and Nucleosynthesis in honor of David L. Lambert
Page: 367
Authors: Sterling, N.C.; Dinerstein, H.L.
Abstract: We present results from an ongoing survey of infrared emission lines from the neutron-capture elements Se and Kr in Galactic planetary nebulae (PNe). Se and Kr may be produced in the initial steps of the s-process during the asymptotic giant branch (AGB) phase of PN progenitor stars, and brought to the surface by convective dredge-up before PN ejection. Therefore, enriched Se and Kr abundances in PNe indicate that the s-process and dredge-up were active within the progenitor stars. We have detected the emission lines [Kr III] 2.199 and [Se IV] 2.287 μm in 68 of 119 Galactic PNe, and used these line fluxes to derive ionic and total elemental abundances. Using the ionization correction factors Se3+/Se ≈ Ar++/Ar and Kr++/Kr ≈ S++/S, we find a range of Se and Kr abundances, from nearly solar to enriched by a factor of 5-10 times, which implies varying degrees of dredge-up efficiency in the progenitor stars. We have searched for correlations between n-capture element abundances and other nebular properties, and find that PNe with Wolf-Rayet central stars tend to exhibit more elevated Se and Kr abundances than other nebulae. Bipolar nebulae, believed to arise from the most massive of PN progenitors, may have lower n-capture abundances than elliptical PNe.
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