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We present new fluorine abundance estimations in two carbon enhancedmetal-poor (CEMP) stars, HE 1429-0551 and HE 1305+0007. HE 1429-0551 is alsoenriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE1305+0007 is enhanced in both, slow and rapid neutron-capture process elements,a CEMP-s/r. The F abundances estimates are derived from the vibration-rotationtransition of the HF molecule at 23358.6 A using high-resolution infraredspectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) atthe 4m-class Lowell Discovery Telescope. Our results include a F abundancemeasurement in HE 1429-0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = -2.53,and a F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H]= -2.28. Our new derived F abundance in HE 1429-0551 makes this object the mostmetal-poor star where F has been detected. We carefully compare these resultswith literature values and state-of-the-art CEMP-s model predictions includingdetailed AGB nucleosynthesis and binary evolution. The modelled fluorineabundance for HE 1429-0551 is within reasonable agreement with our observedabundance, although is slightly higher than our observed value. For HE1429-0551, our findings support the scenario via mass transfer by a primarycompanion during its thermally-pulsing phase. Our estimated upper limit in HE1305+0007, along with data from the literature, shows large discrepanciescompared with AGB models. The discrepancy is principally due to thesimultaneous s- and r-process element enhancements which the model struggles toreproduce.

Constraining Nucleosynthesis in Two CEMP Progenitors Using Fluorine