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    The Abundances of Light Neutron-Capture Elements in Planetary Nebulae. III. The Impact of New Atomic Data on Nebular Selenium and Krypton Abundance Determinations

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    Date
    2015-06
    Author
    Sterling, N. C.
    Porter, R. L.
    Dinerstein, Harriet L.
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    Abstract
    The detection of neutron(n)-capture elements in several planetary nebulae (PNe) has provided a new means of investigating s-process nucleosynthesis in low-mass stars. However, a lack of atomic data has inhibited accurate trans-iron element abundance determinations in astrophysical nebulae. Recently, photoionization (PI) and recombination data were determined for Se and Kr, the two most widely detected n-capture elements in nebular spectra. We have incorporated these new data into the photoionization code Cloudy. To test the atomic data, numerical models were computed for 15 PNe that exhibit emission lines from multiple Kr ions. We found systematic discrepancies between the predicted and observed emission lines that are most likely caused by inaccurate PI and recombination data. These discrepancies were removed by adjusting the Kr+-Kr3+ PI cross sections within their cited uncertainties and the dielectronic recombination rate coefficients by slightly larger amounts. From grids of models spanning the physical conditions encountered in PNe, we derive new, broadly applicable ionization correction factor (ICF) formulae for calculating Se and Kr elemental abundances. The ICFs were applied to our previous survey of near-infrared [Kr III] and [Se IV] emission lines in 120 PNe. The revised Se and Kr abundances are 0.1-0.3 dex lower than former estimates, with average values of [Se/(O, Ar)] = 0.12 +/- 0.27 and [Kr/(O, Ar)] = 0.82 +/- 0.29, but correlations previously found between their abundances and other nebular and stellar properties are unaffected. We also find a tendency for high-velocity PNe that can be associated with the Galactic thick disk to exhibit larger s-process enrichments than low-velocity PNe belonging to the thin-disk population.
    Department
    Astronomy
    Subject
    atomic data
    infrared: general
    nuclear reactions, nucleosynthesis,
    abundances
    planetary nebulae: general
    stars: agb and post-agb
    asymptotic giant branch
    optical recombination lines
    near-infrared
    spectroscopy
    s-process abundances
    metal-poor stars
    effective
    collision strengths
    high-resolution spectroscopy
    sagittarius dwarf
    galaxy
    massive agb evolution
    wc central stars
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/43068
    Citation
    Sterling, N. C., R. L. Porter, and Harriet L. Dinerstein. "The Abundances of Light Neutron-Capture Elements in Planetary Nebulae III. The Impact of New Atomic Data on Nebular Selenium and Krypton Abundance Determinations." arXiv preprint arXiv:1505.01162 (Jun., 2015).
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    • facebook
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