Improved Neutron-Capture Element Abundances in Planetary Nebulae from Multi-Wavelength Spectroscopy and New Atomic Data

Details Improved Neutron-Capture Element Abundances in Planetary Nebulae from Multi-Wavelength Spectroscopy and New Atomic Data Improved Neutron-Capture Element Abundances in Planetary Nebulae from Multi-Wavelength Spectroscopy and New Atomic Data

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21110010s&link_type=abstract

American Astronomical Society, AAS Meeting #211, #100.10; Bulletin of the American Astronomical Society, Vol. 39, p.913

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The accurate determination of neutron(n)-capture element abundances in planetary nebulae (PNe) provides valuable information regarding s-process nucleosynthesis and convective dredge-up in PN progenitor stars. Sterling & Dinerstein (2007, ApJS, in press, astro-ph/0706.1074) determined the abundances of the n-capture elements Se and Kr in 120 PNe to accuracies of a factor of two or three. The abundance uncertainties arose primarily from: (1) the detection of only one ion of each element, leading to large and uncertain ionization correction factors (ICFs); and (2) the lack of atomic data governing the Se and Kr ionization balance.
We present preliminary results from a study that aims to improve the accuracy of n-capture element abundances in PNe, utilizing new observational measurements and atomic data determinations. We have obtained deep, high resolution optical spectra of 12 s-process enriched PNe selected from the sample of Sterling & Dinerstein, in order to search for emission lines of additional Se and Kr ions as well as other n-capture elements (e.g., Br and Xe). These measurements allow multiple ions of trans-iron elements to be detected, which reduces the uncertainties in the ICFs and consequently in the derived elemental abundances. In addition, we discuss ongoing calculations of photoionization cross-sections and recombination rate coefficients of Se, Kr, and Xe ions using the atomic structure codes AUTOSTRUCTURE (Badnell 1986, J. Phys. B, 19, 3827) and DARC (Ballance & Griffin 2006, J. Phys. B, 40, 3617). These calculations are complemented by absolute photoionization cross-section measurements performed at the Advanced Light Source synchrotron radiation facility. The new atomic data enable accurate ICFs to be derived for these elements, with the aid of photoionization models. We will use these results to determine the abundances of n-capture elements in PNe more accurately than previously possible, and to study the details of s-process nucleosynthesis in their progenitor stars.

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