Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
David A. Neufeld
(1)
,
Javier R. Goicoechea
(2)
,
Paule Sonnentrucker
(1)
,
John H. Black
(3)
,
John C. Pearson
(4)
,
Shanshan Yu
(4)
,
Thomas G. Phillips
(5)
,
Darek C. Lis
(5)
,
Massimo de Luca
(6, 7, 8)
,
Eric Herbst
(9)
,
P. B. Rimmer
(9)
,
Maryvonne Gerin
(6, 7, 8)
,
Tom A. Bell
(5)
,
Francois Boulanger
(10)
,
José Cernicharo
(2)
,
A. Coutens
(11, 12)
,
Emmanuel Dartois
(10)
,
M. Kazmierczak
(13)
,
Pierre J. Encrenaz
(6, 7, 8)
,
Edith Falgarone
(6, 7, 8)
,
Thomas R. Geballe
(14)
,
T. Giesen
(15)
,
Benjamin Godard
(6, 7, 8)
,
Paul F. Goldsmith
(4)
,
Cecile Gry
(16)
,
Harshal Gupta
(4)
,
Patrick Hennebelle
(6, 7, 8)
,
Pierre Hily-Blant
(17)
,
Christine Joblin
(11, 12)
,
R. Kolos
(18)
,
J. Krelowski
(13)
,
Jesus Martin-Pintado
(2)
,
Karl M. Menten
(19)
,
Raquel Monje
(5)
,
Bhaswati Mookerjea
(20)
,
Michel Pérault
(6, 7, 8)
,
C. M. Persson
(3)
,
René Plume
(21)
,
Morvan Salez
(6, 7, 8)
,
S. Schlemmer
(15)
,
M. Schmidt
(22)
,
J. Stutzki
(15)
,
David Teyssier
(23)
,
Charlotte Vastel
(11, 12)
,
A. Cros
(11, 12)
,
Karl-Ludwig Klein
(24)
,
A. Lorenzani
(25)
,
S. Philipp
(26)
,
L. A. Samoska
(4)
,
Russell Shipman
(27)
,
A. Tielens
(28)
,
Ryszard Szczerba
(22)
,
J. Zmuidzinas
(5)
1
JHU -
Johns Hopkins University
2 CAB - Centro de Astrobiología, Consejo Superior de Investigaciones Científicas (CSIC)/Instituto Nacional de Técnica Aeroespacial (INTA)
3 Chalmers University of Technology
4 JPL - Jet Propulsion Laboratory
5 Cahill Center for Astronomy and Astrophysics
6 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
7 Instrumentation et télédétection
8 Dynamique des milieux interstellaires et plasmas stellaires
9 OSU - The Ohio State University [Columbus]
10 IAS - Institut d'astrophysique spatiale
11 UT - Université de Toulouse
12 CESR - Centre d'étude spatiale des rayonnements
13 Nicolaus Copernicus University [Toruń]
14 Gemini telescope, Hilo
15 Physikalisches Institut, Universität zu Köln
16 LAM - Laboratoire d'Astrophysique de Marseille
17 LAOG - Laboratoire d'Astrophysique de Grenoble
18 Institute of Physical Chemistry, Polish Academy of Sciences
19 MPIfR - Max-Planck-Institut für Radioastronomie
20 TIFR - Tata Institute of Fundamental Research
21 University of Calgary
22 CAMK - Centrum Astronomiczne im. M. Kopernika, Warszawa
23 ESAC - European Space Astronomy Centre
24 University of Waterloo [Waterloo]
25 OAA - INAF - Osservatorio Astrofisico di Arcetri
26 DLR - Deutsches Zentrum für Luft- und Raumfahrt
27 SRON - SRON Netherlands Institute for Space Research
28 Sterrewacht Leiden, Leiden University
2 CAB - Centro de Astrobiología, Consejo Superior de Investigaciones Científicas (CSIC)/Instituto Nacional de Técnica Aeroespacial (INTA)
3 Chalmers University of Technology
4 JPL - Jet Propulsion Laboratory
5 Cahill Center for Astronomy and Astrophysics
6 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
7 Instrumentation et télédétection
8 Dynamique des milieux interstellaires et plasmas stellaires
9 OSU - The Ohio State University [Columbus]
10 IAS - Institut d'astrophysique spatiale
11 UT - Université de Toulouse
12 CESR - Centre d'étude spatiale des rayonnements
13 Nicolaus Copernicus University [Toruń]
14 Gemini telescope, Hilo
15 Physikalisches Institut, Universität zu Köln
16 LAM - Laboratoire d'Astrophysique de Marseille
17 LAOG - Laboratoire d'Astrophysique de Grenoble
18 Institute of Physical Chemistry, Polish Academy of Sciences
19 MPIfR - Max-Planck-Institut für Radioastronomie
20 TIFR - Tata Institute of Fundamental Research
21 University of Calgary
22 CAMK - Centrum Astronomiczne im. M. Kopernika, Warszawa
23 ESAC - European Space Astronomy Centre
24 University of Waterloo [Waterloo]
25 OAA - INAF - Osservatorio Astrofisico di Arcetri
26 DLR - Deutsches Zentrum für Luft- und Raumfahrt
27 SRON - SRON Netherlands Institute for Space Research
28 Sterrewacht Leiden, Leiden University
A. Coutens
- Fonction : Auteur
- PersonId : 739468
- IdHAL : audrey-coutens
- ORCID : 0000-0003-1805-3920
- IdRef : 167181491
Emmanuel Dartois
- Fonction : Auteur
- PersonId : 741313
- IdHAL : emmanuel-dartois
- ORCID : 0000-0003-1197-7143
- IdRef : 136696686
Benjamin Godard
- Fonction : Auteur
- PersonId : 1379031
- ORCID : 0000-0003-0060-8887
- IdRef : 144711060
Patrick Hennebelle
- Fonction : Auteur
- PersonId : 950937
- ORCID : 0000-0002-0472-7202
- IdRef : 161792030
Christine Joblin
- Fonction : Auteur
- PersonId : 21867
- IdHAL : christine-joblin
- ORCID : 0000-0003-1561-6118
- IdRef : 052563693
Résumé
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 111-000 transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s-1 with respect to the local standard of rest. The inferred OH+/H2O+ 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 H2O+ 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 H3+ and other species.