Strong absorption by interstellar hydrogen fluoride: Herschel/HIFI observations of the sight-line to G10.6-0.4 (W31C)
Journal article, 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, accompanied by strong absorption by foreground material at LSR velocities in the range 15 to 50 km/s. The spectrum is similar to that of the 1113.3430 GHz 1(11)-0(00) 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 1.6E+14 cm-2 on the HF column density along the sight-line to G10.6-0.4. Our lower limit on the HF abundance, 6E-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.
Author
D.A. Neufeld
P. Sonnentrucker
T.G. Phillips
D. Lis
M. de Luca
J. R. Goicoechea
John H Black
M. Gerin
T. A. Bell
F. Boulanger
J. Cernicharo
A. Coutens
E. Dartois
M. Kazmierczak
P. Encrenaz
E. Falgarone
Thomas Geballe
T. Giesen
B. Godard
P.F. Goldsmith
C. Gry
H. Gupta
P. Hennebelle
E. Herbst
P. Hily-Blant
C. Joblin
R. Kolos
J. Krelowski
J. Martin-Pintado
K.M. Menten
Raquel Monje
B. Mookerjea
T. J. Pearson
M. Perault
Carina Persson
R. Plume
M. Salez
S. Schlemmer
M. Schmidt
J. Stutzki
D. Teyssier
C. Vastel
S. Yu
P. Cais
E. Caux
René Liseau
P. Morris
P. Planesas
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 518 4 108- L108Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201014523