Abstract

About half the Solar System inventory of trans-iron elements were created through slow neutron capture reactions, some of which took place in evolved low-mass stars while on the late Asymptotic Giant Branch (AGB). The envelopes of these stars are expelled via planetary nebulae and contribute to the chemical evolution of the Galaxy. We have been using infrared spectroscopy with instruments such as IGRINS on the McDonald Observatory 2.7m to measure s-process enrichments of several elements in planetary nebulae. In this talk I report recent discoveries of new infrared lines from the light s-process products Br and Rb (atomic numbers 35 and 37) with iSHELL on the IRTF, and from the heavier elements Te and Xe (52 and 54) with HPF on the HET. These lines will provide new information on AGB nucleosynthesis and the origin of the trans-iron elements.