# # Program information file # PROGRAM_ID 2023A045 PROGRAM_TITLE Fluorine Abundances in AGB Carbon Stars PROGRAM_INV1 Kristin Brady PROGRAM_INV2 Catherine Pilachowski PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG The abundances of light elements provide insight into the chemical evolution of the Milky Way Galaxy and its stellar populations. Understanding the formation of odd elements provides an opportunity to constrain nucleosynthesis processes as, for example, 19F [the lone stable isotope of fluorine] is integral in proton capture reactions that include the CNO and Ne-Na cycles. The light, odd-Z element fluorine is thought to be produced in multiple stellar sites, with AGB stars among the most significant sources for the galactic fluorine abundance. However, the observed excess of fluorine in AGB stars surprisingly relies heavily on measurements of stars with a C/O ratio of approximately 1. On a plot of [F/Fe] vs. C/O for known AGB stars from the literature with F, C, and O abundances, there is a spike in the fluorine abundance at a C/O ratio of 1, while the fluorine abundance is below solar for lower and higher C/O ratio values. We propose to observe 12 AGB carbon stars with iSHELL to measure their fluorine abundances, with the goal of understanding the peculiar spike in fluorine abundance at C/O = 1. Fluorine abundances will be measured using the HF feature at 23358.329 A. The selected AGB stars have C/O ratios spanning a range from 1.1-1.76, which will sufficiently define the previously unexplored gap in fluorine abundance measurements for the C/O > 1.1 range. PROGRAM_ABSTRACT_END