Issue |
A&A
Volume 518, July-August 2010
Herschel: the first science highlights
|
|
---|---|---|
Article Number | L108 | |
Number of page(s) | 5 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201014523 | |
Published online | 16 July 2010 |
Letter to the Editor
Strong absorption by interstellar hydrogen fluoride: Herschel/HIFI observations of the sight-line to G10.6–0.4 (W31C)*
1
The Johns Hopkins University, Baltimore, MD 21218, USA e-mail: neufeld@pha.jhu.edu
2
California Institute of Technology, Pasadena, CA 91125, USA
3
LERMA, CNRS, Observatoire de Paris and ENS, France
4
Centro de Astrobiologìa, CSIC-INTA, 28850, Madrid, Spain
5
Chalmers University of Technology, Göteborg, Sweden
6
Institut d'Astrophysique Spatiale (IAS), Orsay, France
7
Université Toulouse; UPS; CESR; and CNRS; UMR5187,
9 avenue du colonel Roche, 31028 Toulouse Cedex 4, France
8
Nicolaus Copernicus University, Torun, Poland
9
Gemini telescope, Hilo, Hawaii, USA
10
I. Physikalisches Institut, University of Cologne, Germany
11
JPL, California Institute of Technology, Pasadena, USA
12
LAM, OAMP, Université Aix-Marseille & CNRS, Marseille, France
13
Depts. of Physics, Astronomy & Chemistry, Ohio State Univ., USA
14
Laboratoire d'Astrophysique de Grenoble, France
15
Institute of Physical Chemistry, PAS, Warsaw, Poland
16
MPI für Radioastronomie, Bonn, Germany
17
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
18
Dept. of Physics & Astronomy, University of Calgary, Canada
19
Nicolaus Copernicus Astronomical Center, Poland
20
European Space Astronomy Centre, ESA, Madrid, Spain
21
Institute Université de Bordeaux & CNRS, Bordeaux, France
22
Observatorio Astron. Nacional (IGN) and ALMA, Santiago, Chile
Received:
27
March
2010
Accepted:
12
April
2010
We report the detection of strong absorption by interstellar hydrogen fluoride along the sight-line to the submillimeter continuum source G10.6–0.4 (W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 1232.4763 GHz J = 1–0 HF transition in the upper sideband of the Band 5a receiver. The resultant spectrum shows weak HF emission from G10.6–0.4 at LSR velocities in the range –10 to –3 km s-1, accompanied by strong absorption by foreground material at LSR velocities in the range 15 to 50 km s-1. The spectrum is similar to that of the 1113.3430 GHz 111–000 transition of para-water, although at some frequencies the HF (hydrogen fluoride) optical depth clearly exceeds that of para-H2O. The optically-thick HF absorption that we have observed places a conservative lower limit of 1.6×1014 cm-2 on the HF column density along the sight-line to G10.6–0.4. Our lower limit on the HF abundance, 6×10-9 relative to hydrogen nuclei, implies that hydrogen fluoride accounts for between ~30% and 100% of the fluorine nuclei in the gas phase along this sight-line. This observation corroborates theoretical predictions that – because the unique thermochemistry of fluorine permits the exothermic reaction of F atoms with molecular hydrogen – HF will be the dominant reservoir of interstellar fluorine under a wide range of conditions.
Key words: ISM: molecules / submillimeter: ISM / molecular processes
© ESO, 2010
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