Fluorine Abundances in the Orion Nebula Cluster

This study uses cool dwarfs as sources with which to probe fluorineabundances via HF. This molecule is detected for the first time in young K-Mdwarf members of an OB association. Fluorine, oxygen, and carbon abundanceswere derived from the HF(1--0) R9 line along with samples of OH and COvibration-rotation lines present in high-resolution infrared spectra observedwith the Phoenix spectrograph on the Gemini South Telescope. The fluorine andoxygen results obtained for these targets, still in the pre-main-sequence stageof evolution, agree well with the general trend defined for the Milky Way disk;the latter being deduced from observations of more evolved giant stars. Inaddition, the carbon and oxygen abundances obtained for the studied starsoverlap results from previous studies of the more massive OB stars and FG dwarfmembers of the Orion Nebula Cluster. We conclude from this agreement that thefluorine abundances derived for the Orion K-M dwarfs (when there is noconspicuous evidence of disks) can be considered a good representation of thecurrent fluorine abundance value for the Milky Way disk.Comment: 18 pages, including 2 tables and 3 figures. Accepted for publication in The Astrophysical Journa