Neutron-capture elements in planetary nebulae: Identification of two near-infrared emission lines as [Kr III] and [Se IV]

I propose that two previously unidentified lines at 2.199 and 2.287 mum see n in the spectra of planetary nebulae (PNs) are fine-structure transitions of Kr+2 and Se+3. These are the cosmically most abundant elements with Z > 32. The ionic stages and originating energy levels of the observed transiti ons are expected to be significantly populated under nebular conditions, an d these elements-especially the noble gas Kr- are unlikely to be strongly d epleted out of the gas phase into grains. Furthermore, their concentrations can be enhanced by s-processing, which occurs in the interiors of the PN p rogenitor stars. The observed line strengths are consistent with modest (fa ctor of a few) overabundances. In support of the identification of the 2.19 9 mum line as [Kr III], P-3(1)-P-3(2), PNs that display this line also show [Kr III] D-1(2)-P-3(2) 6828 Angstrom emission. I identify the 2.287 mum li ne as [Se IV] P-2(3/2)-P-2(1/2). These identifications suggest a new range of possibilities for line identifications in the infrared. In addition, the observability of emission lines from n-capture species introduces a novel approach for studying advanced evolutionary stages and nucleosynthesis in t he progenitor stars and for more fully delineating the role of PNs as agent s of galactic chemical enrichment.