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Title: THE ABUNDANCES OF LIGHT NEUTRON-CAPTURE ELEMENTS IN PLANETARY NEBULAE. III. THE IMPACT OF NEW ATOMIC DATA ON NEBULAR SELENIUM AND KRYPTON ABUNDANCE DETERMINATIONS

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{sup +}–Kr{sup 3+} 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 formermore » 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.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Physics, University of West Georgia, 1601 Maple Street, Carrollton, GA 30118 (United States)
  2. Department of Physics and Astronomy and Center for Simulational Physics, University of Georgia, Athens, GA 30602 (United States)
  3. Department of Astronomy, University of Texas, 2515 Speedway, C1400, Austin, TX 78712-1205 (United States)
Publication Date:
OSTI Identifier:
22520192
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 218; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; CAPTURE; CORRELATIONS; CROSS SECTIONS; ELEMENT ABUNDANCE; IRON; KRYPTON; KRYPTON IONS; NEUTRON REACTIONS; NUCLEOSYNTHESIS; PHOTOIONIZATION; PLANETARY NEBULAE; RECOMBINATION; S PROCESS; SELENIUM; STARS; VISIBLE RADIATION