Despite the importance of measuring the interstellar fluorine abundance only three previous detection has been made due to the low relative abundance of fluorine, the lack of lines outside the far-ultraviolet, and blending of the available transitions with lines of molecular hydrogen. The nucleosynthetic source(s) of fluorine are still a matter of debate, and the present day abundance of fluorine can potentially constrain models for its production. Furthermore, due to its extreme reactivity, measurement of the gas-phase interstellar fluorine abundance is important for models of gas and grain chemistry.We report on the results of high S/N-ratio (50-100) FUSE observations of the interstellar absorption lines of neutral fluorine at 951 and 954 Angstroms toward two distant Galactic stars (HD 103779 and HD 164816). The sightline toward HD 103779 lies near the edge of the North Polar Spur and Radio Loop 1. HD 164816 is associated with the Lagoon nebula (M 8) at a distance of about 1.5 kpc, and also probes both distant and local gas. Modeling of both interstellar and stellar absorption lines has been used to determine the abundance from the (blended) strong fluorine line at 954.83 Angstroms. We have also made a sensitive search for the weaker line at 951.87 Angstroms to provide a consistency check for our models, and have made a tentative detection toward HD 103779. While preliminary analysis of these data suggests that the observed fluorine gas-phase abundances (and hence inferred depletions) are roughly consistent with previous measures toward delta Sco (Copernicus) and two stars in Cep OB2 (FUSE), there may be a slight enhancement in the gas-phase abundance toward HD 103779. This research was supported by NASA grant NAG5-13005.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2004