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Article << Previous     |     Next >>   Contents Vol 26(3)

Improved Neutron-Capture Element Abundances in Planetary Nebulae

N. C. Sterling A I, H. L. Dinerstein B, S. Hwang B, S. Redfield C, A. Aguilar D, M. C. Witthoeft A, D. Esteves E, A. L. D. Kilcoyne D, M. Bautista F, R. Phaneuf E, R. C. Bilodeau D, C. P. Ballance G, B. McLaughlin H, P. H. Norrington H

A NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
B University of Texas, Department of Astronomy, 1 University Station, C1400, Austin, TX 78712-0259, USA
C Astronomy Department, Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
D Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, MS: 6R2100, University of California, Berkeley, CA 94270, USA
E Department of Physics, MS 220, University of Nevada, Reno, NV 89557-0058, USA
F Virginia Polytechnic Institute & State University, Physics Department, Robeson Hall (0435), Blacksburg, VA 24061, USA
G Department of Physics, Auburn University, Auburn, AL 33333, USA
H Centre for Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen’s University Belfast, The David Bates Building, 7 College Park, Belfast BT7 1NN, UK
I Corresponding author. Email: nicholas.c.sterling@nasa.gov
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Spectroscopy of planetary nebulae (PNe) provides the means to investigate s-process enrichments of neutron(n)-capture elements that cannot be detected in Asymptotic Giant Branch (AGB) stars. However, accurate abundance determinations of these elements present a challenge. Corrections for unobserved ions can be large and uncertain, since in many PNe only one ion of a given n-capture element has been detected. Furthermore, the atomic data governing the ionization balance of these species are not well-determined, inhibiting the derivation of accurate ionization corrections. We present initial results of a program that addresses these challenges. Deep high-resolution optical spectroscopy of ~20 PNe has been performed to detect emission lines from trans-iron species including Se, Br, Kr, Rb and Xe. The optical spectral region provides access to multiple ions of these elements, which reduces the magnitude and importance of uncertainties in the ionization corrections. In addition, experimental and theoretical efforts are providing determinations of the photoionization cross sections and recombination rate coefficients of Se, Kr and Xe ions. These new atomic data will make it possible to derive robust ionization corrections for these elements. Together, our observational and atomic data results will enable n-capture element abundances to be determined with unprecedented accuracy in ionized nebulae.

Keywords: planetary nebulae: general — nuclear reactions, nucleosynthesis, abundances — stars: AGB and post-AGB — atomic data

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