Issue |
A&A
Volume 521, October 2010
Herschel/HIFI: first science highlights
|
|
---|---|---|
Article Number | L16 | |
Number of page(s) | 7 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201015115 | |
Published online | 01 October 2010 |
Letter to the Editor
Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10.6–0.4 (W31C), W49N, and W51 *,**
1
LERMA, CNRS, Observatoire de Paris and ENS, France e-mail: maryvonne.gerin@ens.fr
2
Centro de Astrobiología, CSIC-INTA, Madrid, Spain
3
Depts. of Physics, Astronomy & Chemistry, Ohio State Univ., USA
4
Institut d'Astrophysique Spatiale (IAS), Orsay, France
5
California Institute of Technology, Pasadena, CA 91125, USA
6
Université de Toulouse; UPS; CESR; 9 avenue du colonel Roche,
31028 Toulouse Cedex 4, France
7
CNRS; UMR5187; 31028 Toulouse, France
8
Nicolaus Copernicus University, Torún, Poland
9
The Johns Hopkins University, Baltimore, MD 21218, USA
10
Chalmers University of Technology, Onsala Space Observatory,
43992 Onsala, Sweden
11
JPL, California Institute of Technology, Pasadena, USA
12
I. Physikalisches Institut, University of Cologne, Germany
13
Laboratoire d'Astrophysique de Marseille (LAM), France
14
Laboratoire d'Astrophysique de Grenoble, France
15
Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland
16
Tata Institute of Fundamental Research, Mumbai, India
17
Dept. of Physics & Astronomy, University of Calgary, Canada
18
Nicolaus Copernicus Astronomical Center, Poland
19
European Space Astronomy Centre, ESA, Madrid, Spain
20
MPI für Extraterrestrische Physik, Garching, Germany
21
MPI für Radioastronomie, Bonn, Germany
22
Gemini telescope, Hilo, Hawaii, USA
23
Infrared Processing and Analysis Center, California
Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
24
SRON Netherlands Institute for Space Research, Netherlands
Received:
31
May
2010
Accepted:
9
July
2010
We report the detection of the ground state
N,J = 1,3/2 1,1/2 doublet of the
methylidyne radical CH at ~532 GHz and ~536 GHz
with the Herschel/HIFI instrument along the
sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and
W51. While the molecular cores associated with these massive star-forming
regions show emission lines, clouds in the
diffuse interstellar medium are detected in absorption
against the strong submillimeter background. The combination of
hyperfine structure with emission and absorption results in complex
profiles, with overlap of the different hyperfine components.
The opacities of most of the CH absorption features
are linearly correlated with those of CCH, CN, and HCO+ in the
same velocity intervals. In specific narrow velocity intervals,
the opacities of
CN and HCO+ deviate from the mean trends, giving
rise to more opaque absorption features.
We propose that CCH can be used
as another tracer of the molecular gas in the absence of better tracers, with
[CCH]/[ H2] ~ 3.2±1.1×10-8.
The observed [CN]/[CH], [CCH]/[CH] abundance ratios
suggest that the bulk of the diffuse matter along the lines of sight
has gas densities nH = n(H) + 2n(H2)
ranging between 100 and 1000 cm-3.
Key words: ISM: clouds / ISM: molecules / submillimeter: ISM / ISM: individual objects: G10.6-0.4 / ISM: individual objects: W49N / ISM: individual objects: W51
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendices A and B (pages 6, 7) are only available in electronic form at http://www.aanda.org
© ESO, 2010
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