Synthesis of 19F in Wolf-Rayet stars

Meynet & Arnould (1993) have suggested that Wolf- Rayet (WR) stars could significantly contaminate the Galaxy with 19 F. In their scenario, 19 F is synthesized at the beginning of the He-burning phase from the 14 N left over by the previous CNO-burning core, and is ejected in the interstellar medium when the star enters its WC phase. Recourse to CNO seeds makes the 19 F yields metallicity-dependent. These yields are calculated on grounds of detailed stellar evolutionary sequences for an extended range of initial masses (from 25 to 120 M) and metallicities (Z =0 :008, 0.02 and 0.04). The adopted mass loss rate prescription enables to ac- count for the observed variations of WR populations in different environments. The 19 F abundance in the WR winds of 60 M model stars is found to be about 10 to 70 times higher than its initial value, depending on the metallicity. This prediction is used in conjunc- tion with a very simple model for the chemical evolution of the Galaxy to predict that WR stars could be significant (dominant?) contributors to the solar system fluorine content. We also briefly discuss the implications of our model on the possible detection of fluorine at high redshift.