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S.R. Federman, Yaron Sheffer (U. Toledo), David L. Lambert (U. Texas), V.V. Smith (UTEP)
Massive stars, through their terminal supernova explosions, seed interstellar clouds with newly synthesized elements. In order to understand the details of chemical evolution in a site of star formation, the interstellar material toward stars in Cep OB2 was studied via absorption lines seen in FUSE spectra. A search for the F~{\small I} resonance lines at 951 and 954 Å\ toward HD~208440 and HD~209339A was conducted to help resolve the origin of this element: is F synthesized primarily in Type II supernovae, whose effects should be revealed in a region of ongoing massive star formation, or in asymptotic giant branch stars? Syntheses of H2 Lyman bands near 1060 Å\ were used to remove H2 absorption in the vicinity of \lambda954, the stronger of the two F~{\small I} lines. In the process, we determined the maximium H2 column density before H2 absorption becomes black in this wavelength region. Our upper limits on \lambda951 are consistent with the measures from the 954 Å\ line. The inferred F abundances are similar to the abundance derived for the gas toward \delta Sco from measurements with the Copernicus satellite.
Further comparisons among elemental abundance ratios were performed to discern the presence of enhanced F in an environment shaped by past SNe~II. First, we obtained the elemental abundance of Cl (from FUSE spectra of Cl~{\small I}~and~{\small II}) to determine the expected amount of F depletion onto grains. Then, we derived the elemental abundances of N~{\small I} and O~{\small I} from FUSE and HST spectra, respectively, because these two elements show modest amounts of depletion and are synthesized through other processes. Our results indicate that the F abundance and the F/O and F/N elemental abundance ratios are not enhanced for the two sight lines studied to date.
This research was supported by NASA grant NAG5-10305 and by the STScI grant associated with the program GO-08693.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.