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Herschel/HIFI observations of interstellar OH^+ and H_2O^+ towards W49N: a probe of diffuse clouds with a small molecular fraction

Neufeld, D. A. and Phillips, T. G. and Lis, D. C. and Bell, T. A. and Monje, R. and Zmuidzinas, J. (2010) Herschel/HIFI observations of interstellar OH^+ and H_2O^+ towards W49N: a probe of diffuse clouds with a small molecular fraction. Astronomy and Astrophysics, 521 . Art. No. L10. ISSN 0004-6361. doi:10.1051/0004-6361/201015077.

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We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel’s HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1–0 transition of OH^+ and the 1115 GHz 1_(11)−0_(00) transition of ortho-H2O+. The resultant spectra show absorption by ortho-H_2O^+, and strong absorption by OH^+, in foreground material at velocities in the range 0 to 70 kms^(−1) with respect to the local standard of rest. The inferred OH^+/H_2O^+ abundance ratio ranges from ~3 to ~15, implying that the observed OH^+ arises in clouds of small molecular fraction, in the 2−8% range. This conclusion is confirmed by the distribution of OH^+ and H_2O^+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH^+/H abundance ratio of a few ×10^(−8) suggests a cosmic ray ionization rate for atomic hydrogen of 0.6−2.4 × 10^(−16) s^(−1), in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H^+_3 and other species.

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Neufeld, D. A.0000-0001-8341-1646
Lis, D. C.0000-0002-0500-4700
Additional Information:© 2010 ESO. Received 28 May 2010, Accepted 28 June 2010, Published online 01 October 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiologá (CSIC-INTA). Sweden: Chalmers University of Technology – MC2, RSS & GARD;Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. This research was performed, in part, through a JPL contract funded by the National Aeronautics and Space Administration. J.R.G. was supported by a Ramón y Cajal contract and by the MICINN/AYA2009-07304 grant. R. Sz. and M. Sch. acknowledge support from grant No. 203 393334 from Polish MNiSW.
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Ramón y Cajal ProgrammeUNSPECIFIED
Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW)203 393334
Ministerio de Ciencia e Innovación (MICINN)AYA2009-07304
Subject Keywords:ISM: molecules – submillimeter: ISM – astrochemistry – molecular processes
Record Number:CaltechAUTHORS:20110103-145133829
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Official Citation:Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction D. A. Neufeld, J. R. Goicoechea, P. Sonnentrucker, J. H. Black, J. Pearson, S. Yu, T. G. Phillips, D. C. Lis, M. De Luca, E. Herbst, P. Rimmer, M. Gerin, T. A. Bell, F. Boulanger, J. Cernicharo, A. Coutens, E. Dartois, M. Kazmierczak, P. Encrenaz, E. Falgarone, T. R. Geballe, T. Giesen, B. Godard, P. F. Goldsmith, C. Gry, H. Gupta, P. Hennebelle, P. Hily-Blant, C. Joblin, R. Kołos, J. Krełowski, J. Martín-Pintado, K. M. Menten, R. Monje, B. Mookerjea, M. Perault, C. Persson, R. Plume, M. Salez, S. Schlemmer, M. Schmidt, J. Stutzki, D. Teyssier, C. Vastel, A. Cros, K. Klein, A. Lorenzani, S. Philipp, L. A. Samoska, R. Shipman, A. G. G. M. Tielens, R. Szczerba and J. Zmuidzinas A&A 521 L10 (2010) DOI: 10.1051/0004-6361/201015077
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21553
Deposited By: Benjamin Perez
Deposited On:03 Jan 2011 23:23
Last Modified:09 Nov 2021 15:58

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