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Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6542s&link_type=abstract
HST Proposal ID #6542
Other
Hst Proposal Id #6542 Interstellar Medium
Scientific paper
We propose to obtain high signal-to-noise data { 1300} with the GHRS of the weak intersystem line of C II {Lambda2325 Angstrom} toward Kappa Ori and Lambda Ori to determine the limits on the gas-phase abundance of carbon, C/H, in environments where other elements show measurable return from dust to the gas-phase in comparison to moderately dense sight lines like Zeta Oph. In a recent study with the GHRS, we found that the abundance of carbon is remarkably constant in sight lines where the fraction of H in H_2, f{H_2}, ranges between 10^-1 and 1. At the same time however, other elements exhibiting a similar bulk depletion {from solar} show a modest increase in their gas-phase abundance from high-to-low f{H_2}. This increase is observed to continue to significantly lower values of f{H_2} of the order of 10^-5. Since we interpret this increase as the return of matter to the gas from the dust, the lack of variability in the observed C/H would seem to suggest that the carbon-based grains {and/or PAHs} are not easily disrupted. However, the existing C/H data in the moderate-to-low f{H_2} sight lines are not definitive. Determining the gas-phase C/H toward Kappa Ori and Lambda Ori f{H_2} eq 3times10^-5 and 3times10^-2, respectively will set practical limits on the variability of gas-phase C/H in low density gas and the resiliency of the carriers of carbon in non-atomic form. Given the high S/N requirements for this project, this is the last opportunity to achieve these results since such precision weak line work will not be possible with STIS.
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