Title: Identification of Near-Infrared [Se III] and [Kr VI] Emission Lines in Planetary Nebulae,
Abstract: We identify [Se III] 1.0994 micron in the planetary nebula (PN) NGC 5315 and
[Kr VI] 1.2330 micron in three PNe, from spectra obtained with the FIRE
spectrometer on the 6.5-m Baade Telescope. Se and Kr are the two most
widely-detected neutron-capture elements in astrophysical nebulae, and can be
enriched by s-process nucleosynthesis in PN progenitor stars. The detection of
[Se III] 1.0994 micron is particularly valuable when paired with observations
of [Se IV] 2.2858 micron, as it can be used to improve the accuracy of nebular
Se abundance determinations, and allows Se ionization correction factor (ICF)
schemes to be empirically tested for the first time. We present new effective
collision strength calculations for Se^{2+} and Kr^{5+}, which we use to
compute ionic abundances. In NGC 5315, we find that the Se abundance computed
from Se^{3+}/H^+ is lower than that determined with ICFs that incorporate
Se^{2+}/H^+. We compute new Kr ICFs that take Kr^{5+}/H^+ into account, by
fitting correlations found in grids of Cloudy models between Kr ionic fractions
and those of more abundant elements, and use these to derive Kr abundances in
four PNe. Observations of [Se III] and [Kr VI] in a larger sample of PNe, with
a range of excitation levels, are needed to rigorously test the ICF
prescriptions for Se and our new Kr ICFs.