DISCOVERY OF RUBIDIUM, CADMIUM, AND GERMANIUM EMISSION LINES IN THE NEAR-INFRARED SPECTRA OF PLANETARY NEBULAE

作者：Sterling N C^*; Dinerstein Harriet L^*; Kaplan Kyle F^*; Bautista Manuel A^*

来源：Astrophysical Journal Letters, 2016, 819(1): L9.

DOI：10.3847/2041-8205/819/1/L9

• atomic data
• infrared: general
• nuclear reactions, nucleosynthesis, abundances
• planetary nebulae: general
• stars: AGB and post-AGB

We identify [Rb IV]. 1.5973 and [Cd IV]. 1.7204 mu m emission lines in high-resolution (R = 40,000) near-infrared spectra of the planetary nebulae (PNe) NGC 7027 and IC 5117, obtained with the Immersion GRating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at McDonald Observatory. We also identify [Ge VI] 2.1930 mu m in NGC 7027. Alternate identifications for these features are ruled out based on the absence of other multiplet members and/or transitions with the same upper levels. Ge, Rb, and Cd can be enriched in PNe by s-process nucleosynthesis during the asymptotic giant branch stage of evolution. To determine ionic abundances, we calculate [Rb IV] collision strengths and use approximations for those of [Cd IV] and [Ge VI]. Our identification of [Rb IV] 1.5973 mu m is supported by the agreement between Rb3+/H+ abundances found from this line and the 5759.55 angstrom feature in NGC 7027. Elemental Rb, Cd, and Ge abundances are derived with ionization corrections based on similarities in ionization potential ranges between the detected ions and O and Ne ionization states. Our analysis indicates abundances 2-4 times solar for Rb and Cd in both nebulae. Ge is subsolar in NGC 7027, but its abundance is uncertain due to the large and uncertain ionization correction. The general consistency of the measured relative s-process enrichments with predictions from models appropriate for these PNe (2.0-2.5. M-circle dot, [Fe/H] = -0.37) demonstrates the potential of using PN compositions to test s-process nucleosynthesis models.

• 出版日期2016-3-1