Fluorine Abundances in the Galactic Nuclear Star Cluster

Abundances of fluorine (F-19), as well as isotopic ratios of O-16/O-17, are derived in a sample of luminous young (similar to 10(7)-10(8) yr) red giants in the Galactic center (with galactocentric distances ranging from 0.6-30 pc), using high-resolution infrared spectra and vibration-rotation lines of (HF)-F-19 near lambda 2.3 mu m. Five of the six red giants are members of the Nuclear star cluster that orbits the central supermassive black hole. Previous investigations of the chemical evolution of F-19 in Galactic thin and thick-disk stars have revealed that the nucleosynthetic origins of F-19 may be rather complex, resulting from two, or more, astrophysical sites; fluorine abundances behave as a primary element with respect to Fe abundances for thick-disk stars and as a secondary element in thin-disk stars. The Galactic center red giants analyzed fall within the thin-disk relation of F with Fe, having near-solar, to slightly larger, abundances of Fe ([Fe/H] = +0.08 +/- 0.04), with a slight enhancement of the F/Fe abundance ratio ([F/Fe] = +0.28 +/- 0.17). In terms of their F and Fe abundances, the Galactic center stars follow the thin-disk population, which requires an efficient source of F-19 that could be the winds from core-He burning Wolf-Rayet stars, or thermally pulsing AGB stars, or a combination of both. The observed increase of [F/Fe] with increasing [Fe/H] found in thin-disk and Galactic center stars is not predicted by any published chemical evolution models that are discussed, thus a quantitative understanding of yields from the various possible sources of F-19 remains unknown.

Automated summary

Using high-resolution infrared spectra and vibration-rotation lines, the abundances of fluorine (F-19) and isotopic ratios of O-16/O-17 were derived in a sample of red giants in the Galactic center. The red giants in the Galactic center have similar fluorine and iron abundances as stars in the thin-disk population, suggesting a possible origin from core-He burning Wolf-Rayet stars, thermally pulsing AGB stars, or a combination of both. The observed increase of [F/Fe] with increasing [Fe/H] in thin-disk and Galactic center stars cannot be explained by existing chemical evolution models.