The following document lists the file abstract/DNEUFELD_HFLUORID.abs
from catalogue VI/111.
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We propose to follow-up our recent discovery of interstellar hydrogen fluoride with a search for the J=2-1 line of HF in two additional sources: Orion Molecular Cloud 1 (OMC-1) and W51. Previously, we have searched for hydrogen fluoride in the single source Sagittarius B2, and obtained a detection of the HF J=2-1 absorption line at 121.6973 microns (Neufeld et al. 1997, ApJ, 488, L141). This detection marks the first discovery of a fluorine molecule in an interstellar gas cloud and the first time that a new interstellar molecule has been detected at far-infrared wavelengths. The derived HF abundance of 3E-10 inferred from this observation implied that the element fluorine shows a gas-phase depletion factor 50 along the line-of-sight to Sgr B2, given reasonable assumptions about the fluorine chemistry and the total elemental abundance of fluorine. The amount of ISO time previously awarded for this project (4000 sec) did not permit us to observe any source other than Sgr B2. In this request for ISO discretionary time, we propose to follow up the discovery of HF with observations of two other sources that are very bright at far-infrared wavelengths: OMC-1 and W51. By observing hydrogen fluoride in these additional sources and obtaining measurements of (or upper limits on) its abundance, we will obtain valuable constraints upon the fluorine chemistry and fluorine depletion in a variety of interstellar environments within the Galaxy. Because hydrogen fluorine possesses one of the largest rotational constants of any molecule, its rotational spectrum lies entirely shortward of the atmospheric windows within which most molecules show rotational transitions. Ground-based observations of interstellar HF are therefore impossible, and ISO provides the last opportunity for many years to follow-up our recent discovery of HF.