# # Program information file # PROGRAM_ID 2021B053 PROGRAM_TITLE Assessing Planetary Nebulae as Sources of Neutron Capture Element Enrichment PROGRAM_INV1 Harriet Dinerstein PROGRAM_INV2 Nicholas Sterling PROGRAM_INV3 William Vacca PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT galactic/interstellar medium PROGRAM_ABSTRACT_BEG We propose to continue our iSHELL program of observing infrared emission lines from trans-iron [Z > 30] elements in planetary nebulae [PNe]. The abundances of many of these nuclei are elevated in some PNe due to in situ nucleosynthesis by the s-process [slow neutron captures] in their progenitor Asymptotic Giant [AGB] stars. We have pioneered the use of infrared spectroscopy of PNe to observe the s-process products Ge, Se, Br, Kr, Rb, Cd, Te, and Xe, in most cases measured through just one ion per element. Our studies empirically establish the contributions of low mass stars in these elements to galactic chemical evolution and provide unique constraints on uncertain aspects of AGB evolution. We have used iSHELL to access spectral regions not available elsewhere [e.g. L, L', and the long end of J], and have detected three new infrared lines, from ions of Br [Z = 35] and Rb [37], albeit so far in only 1-3 PNe per line. In semester 2021B our objectives are: [1] to measure these new lines in additional PNe, for a larger, more diverse sample; [2] to attempt to detect an additional new line, from another ion of Br; and [3] to determine the Fe metallicity [Fe/H] of PNe for which we find s-process enhancements. We will infer [Fe/H] from observations of a [Zn IV] line in the Lp band which we have demonstrated can be measured with iSHELL even in relatively faint PNe. This is important for robust comparisons of our observational results to models of AGB nucleosynthesis, since the amount of s-process enrichment and relative production of different elements is sensitive to [Fe/H]. PROGRAM_ABSTRACT_END