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The cosmic origin of fluorine is still not well constrained. Severalnucleosynthetic channels at different phases of stellar evolution have beensuggested, but these must be constrained by observations. For this, thefluorine abundance trend with metallicity spanning a wide range is required.Our aim is to determine stellar abundances of fluorine for -1.1<[Fe/H]<+0.4. Wedetermine the abundances from HF lines in infrared K-band spectra (at 2.3microns) of cool giants, observed with the IGRINS and Phoenix high-resolutionspectrographs. We derive accurate stellar parameters for all our observed Kgiants, which is important since the HF lines are very temperature sensitive.We find that [F/Fe] is flat as a function of metallicity at [F/Fe]~0, butincreases as the metallicity increases. The fluorine slope shows a clearsecondary behavior in this metallicity range. We also find that the [F/Ce]ratio is relatively flat for -0.6<[Fe/H]<0, and that for two metal-poor([Fe/H]<-0.8), s-process element enhanced giants, we do not detect an elevatedfluorine abundance. We interpret all these observational constraints toindicate that several major processes are at play for the cosmic budget offluorine over time; from those in massive stars at low metallicities, throughthe asymptotic giant branch-star contribution at -0.6<[Fe/H]<0, to processeswith increasing yields with metallicity at super-solar metallicities. Theorigins of the latter, and whether or not Wolf-Rayet stars and/or novae couldcontribute at super-solar metallicities, is currently not known. To quantifythese observational results, theoretical modelling is required. Moreobservations in the metal-poor region are required to clarify the processesthere.

Fluorine in the solar neighbourhood: the need for several cosmic sources