A ABUNDÂNCIA DE FLÚOR NA VIA LÁCTEA

Abstract

The origin of the element fluorine is not well known, but it is known that this element can be produced in three sites: spallation induced by neutrinos after the core collapse phase of a massive supernova; synthesis during thermal pulses in He - burning in AGB stars; fluorine production in cores of Wolf-Rayet stars in early phases of helium burning. In this work we present abundance results for fluorine in 42 stars of the spectral types K, M, MS, S, N and J of the Galactic disk, 3 stars of the Galactic bulge and 7 stars of the globular cluster M4. For stars in the Galactic disk the fluorine abundances were calculated using the MOOG code in LTE and from published equivalent widths values for R9, R13, R14 and R16 lines of the HF molecule at 2.3 micron. The spectra of the disk stars were observed with the 4m Telescope of the Kitt Peak Observatory and Fourier Transform Spectrometer (FTS) spectrometer. For the stars in the Galactic bulge and the globular cluster M4 fluorine abundances were also calculated using the MOOG code, however via spectral synthesis of the rotational-vibrational R9 line of the HF molecule. The stars in the Galactic bulge and the M4 globular cluster were observed in high resolution with the 8m Telescope of Gemini South and using the Phoenix spectrograph of NOAO (National Optical Astronomy Observatory). Our results indicate a significant reduction in the fluorine abundances of disk stars, the bulge stars and stars in the globular cluster M4 when compared to previous results from the literature. This is understood because of the change in the excitation potentials of the HF lines analyzed in this study in comparison with those used in the previous works. Our fluorine results for the disk stars confirm directly that carbon-stars have high fluorine abundances as they are producers of this element. In the Galactic bulge the majority of our results suggest production in SNe II, although some stars have low values of [F/O] more in agreement with production in AGB stars. We confirm the anti-correlation previously found between fluorine and sodium in the globular cluster M4.