FLUORINE ABUNDANCES OF GALACTIC LOW-METALLICITY GIANTS

Abstract

With abundances and 2{\\sigma} upper limits of fluorine (F) in seven\nmetal-poor field giants, nucleosynthesis of stellar F at low metallicity is\ndiscussed. The measurements are derived from the HF(1-0) R9 line at 23358{\\AA}\nusing nearinfrared K-band high-resolution spectra obtained with CRIRES at the\nVery Large Telescope. The sample reaches lower metallicities than previous\nstudies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13.\nEffects of three-dimensional model atmospheres on the derived F and O\nabundances are quantitatively estimated and shown to be insignificant for the\nprogram stars. The observed F yield in the form of [F/O] is compared with two\nsets of Galactic chemical evolution models, which quantitatively demonstrate\nthe contribution of Type II supernova (SN II) {\\nu}-process and asymptotic\ngiant branch/Wolf-Rayet stars. It is found that at this low-metallicity region,\nmodels cannot well predict the observed distribution of [F/O], while the\nobservations are better fit by models considering an SN II {\\nu}-process with a\nneutrino energy of E_{\\nu} = 3 x 10^53 erg. Our sample contains HD 110281, a\nretrograde orbiting low-{\\alpha} halo star, showing a similar F evolution as\nglobular clusters. This supports the theory that such halo stars are possibly\naccreted from dwarf galaxy progenitors of globular clusters in the halo.\n