Herschel observations of the hydroxyl radical (OH) in young stellar objects
Journal article, 2010
Aims: \ldquoWater In Star-forming regions with Herschel\rdquo (WISH) is a Herschel key program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H_2O. High-temperature (T \gap 250 K) chemistry connects OH and H_2O through the OH + H_2 Leftrightarrow H_2O + H reactions. Formation of H_2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H_2O through H_2O + γ_UV Rightarrow OH + H.
Methods: High-resolution spectroscopy of the 163.12 µm triplet of OH towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory. The low- and intermediate-mass protostars HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) on Herschel in four transitions of OH and two [O i] lines.
Results: The OH transitions at 79, 84, 119, and 163 µm and [O i] emission at 63 and 145 µm were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 µm was detected in absorption. With HIFI, the 163.12 µm was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM \gap 11 km s^-1) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [O i] flux and the bolometric luminosity, as found in our sample. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different physical properties of the sources.
ISM: jets and outflows
ISM: molecules
ISM: individual objects: HH 46
astrochemistry
stars: formation
Author
S. F. Wampfler
Swiss Federal Institute of Technology in Zürich (ETH)
G. J. Herczeg
Max Planck Society
S. Bruderer
Swiss Federal Institute of Technology in Zürich (ETH)
A. O. Benz
Swiss Federal Institute of Technology in Zürich (ETH)
E. F. van Dishoeck
Max Planck Society
Leiden University
L. Kristensen
Leiden University
R. Visser
Leiden University
S. Doty
Denison University
M. Melchior
University of Applied Sciences and Arts Northwestern Switzerland
Swiss Federal Institute of Technology in Zürich (ETH)
T. A. van Kempen
Harvard-Smithsonian Center for Astrophysics
U. A. Yildiz
Leiden University
C. Dedes
Swiss Federal Institute of Technology in Zürich (ETH)
J. R. Goicoechea
Centro de Astrobiologia (CAB)
A. Baudry
Laboratoire d'Astrophysique de Bordeaux
Institut National des Sciences de l'Univers
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
R. Bachiller
Spanish National Observatory (OAN)
M. Benedettini
University of Rome Tor Vergata
E. A. Bergin
University of Michigan
Per Bjerkeli
Chalmers, Earth and Space Sciences, Onsala Space Observatory
G. A. Blake
California Institute of Technology (Caltech)
S. Bontemps
Laboratoire d'Astrophysique de Bordeaux
Institut National des Sciences de l'Univers
J. Braine
Institut National des Sciences de l'Univers
Laboratoire d'Astrophysique de Bordeaux
P. Caselli
University of Leeds
Arcetri Astrophysical Observatory
J. Cernicharo
Centro de Astrobiologia (CAB)
C. Codella
Arcetri Astrophysical Observatory
F. Daniel
Centro de Astrobiologia (CAB)
A. M. di Giorgio
University of Rome Tor Vergata
C. Dominik
Anton Pannekoek Institute for Astronomy
Radboud University
P. Encrenaz
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
M. Fich
University of Waterloo
A. Fuente
Spanish National Observatory (OAN)
T. Giannini
Osservatorio Astronomico di Roma
T. de Graauw
Netherlands Institute for Space Research (SRON)
F. Helmich
Netherlands Institute for Space Research (SRON)
F. Herpin
Institut National des Sciences de l'Univers
Laboratoire d'Astrophysique de Bordeaux
M. R. Hogerheijde
Leiden University
T. Jacq
Laboratoire d'Astrophysique de Bordeaux
Institut National des Sciences de l'Univers
D. Johnstone
National Research Council Canada
University of Victoria
J. K. Jorgensen
University of Copenhagen
B. Larsson
Stockholm University
D. Lis
California Institute of Technology (Caltech)
René Liseau
Chalmers, Department of Radio and Space Science, Radio Astronomy and Astrophysics
M. Marseille
Netherlands Institute for Space Research (SRON)
C. McCoey
University of Waterloo
Western University
D. A. Neufeld
Johns Hopkins University
B. Nisini
Osservatorio Astronomico di Roma
Michael Olberg
Chalmers, Department of Radio and Space Science, Radio Astronomy and Astrophysics
B. Parise
Max Planck Society
J. C. Pearson
California Institute of Technology (Caltech)
R. Plume
University of Calgary
C. Risacher
Netherlands Institute for Space Research (SRON)
J. Santiago-García
Institut de Radioastronomie Millimétrique (IRAM)
P. Saraceno
University of Rome Tor Vergata
R. Shipman
Netherlands Institute for Space Research (SRON)
M. Tafalla
Spanish National Observatory (OAN)
F. F. S. van der Tak
Netherlands Institute for Space Research (SRON)
University of Groningen
F. Wyrowski
Max Planck Society
P. Roelfsema
Netherlands Institute for Space Research (SRON)
W. Jellema
Netherlands Institute for Space Research (SRON)
P. Dieleman
Netherlands Institute for Space Research (SRON)
E. Caux
University of Toulouse
Institut National des Sciences de l'Univers
J. Stutzki
University of Cologne
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 521 1 Art. Nr. L36- L36Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1051/0004-6361/201015112