J/ApJ/769/48 Water maser in Orion-KL with Herschel (Neufeld+, 2013)
Herschel/HIFI observations of a new interstellar water maser:
the 532-441 transition at 620.701 GHz.
Neufeld D.A., Wu Y., Kraus A., Menten K.M., Tolls V., Melnick G.J., Nagy Z.
<Astrophys. J., 769, 48 (2013)>
=2013ApJ...769...48N 2013ApJ...769...48N
ADC_Keywords: Masers ; Radio lines ; Interstellar medium
Keywords: ISM: molecules; masers; molecular processes; submillimeter: ISM
Abstract:
Using the Herschel Space Observatory's Heterodyne Instrument for the
Far-Infrared, we have performed mapping observations of the 620.701GHz
532-441 transition of ortho-H2O within a ∼1.5'x1.5' region
encompassing the Kleinmann-Low nebula in Orion (Orion-KL), and pointed
observations of that transition toward the Orion South condensation
and the W49N region of high-mass star formation. Using the Effelsberg
100m radio telescope, we obtained ancillary observations of the
22.23508GHz 616-523 water maser transition; in the case of
Orion-KL, the 621GHz and 22GHz observations were carried out within
10days of each other. The 621GHz water line emission shows clear
evidence for strong maser amplification in all three sources,
exhibiting narrow (∼1km/s FWHM) emission features that are coincident
(kinematically and/or spatially) with observed 22GHz features.
Moreover, in the case of W49N --for which observations were available
at three epochs spanning a 2yr period-- the spectra exhibited
variability. The observed 621GHz/22GHz line ratios are consistent with
a maser pumping model in which the population inversions arise from
the combined effects of collisional excitation and spontaneous
radiative decay, and the inferred physical conditions can plausibly
arise in gas heated by either dissociative or non-dissociative shocks.
The collisional excitation model also predicts that the 22GHz
population inversion will be quenched at higher densities than that of
the 621GHz transition, providing a natural explanation for the
observational fact that 22GHz maser emission appears to be a necessary
but insufficient condition for 621GHz maser emission.
Description:
Our Herschel/HIFI observations of Orion-KL were carried out on 2011
March 11 as part of the "Orion Small Maps" subprogram within the HEXOS
Guaranteed Time Key Program (GTKP; PI: E. Bergin). The beam size was
34" (HPBW), and the absolute pointing accuracy is 2".
On 2011 March 21, 10 days after the Herschel observations of Orion-KL
were performed, we used the Effelsberg 100m telescope to carry out
observations of the 22.23508GHz 616-523 transition, with the goal of
determining the 621GHz/22GHz line flux ratio as a constraint upon
models for the maser emission mechanism.
Objects:
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RA (2000) DE Designation(s)
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5 35 14.31 -5 22 23.2 Orion-KL = NAME ORION-KL
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* Position of Herschel/HIFI map center.
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 24 339 22GHz H2O masers in Orion-KL
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See also:
VI/139 : Herschel Observation Log (Herschel Science Centre, 2013)
J/ApJ/769/20 : 22GHz H2O maser survey toward IR sources (Yung+, 2013)
J/ApJS/156/127 : 350µm molecular line survey of Orion KL (Comito+, 2005)
J/ApJS/155/577 : H2O masers in W49 North and Sagittarius B2 (McGrath+, 2004)
J/A+AS/139/545 : 1-22 GHz spectra survey (Kovalev+, 1999)
J/ApJ/493/940 : Water masers in Orion (Gaume+, 1998)
J/ApJ/393/149 : W49N H2O maser outflow: distance and kinematics (Winn+, 1992)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 F5.1 km/s VLSR [-32/52] Local Standard of Rest velocity
7- 11 F5.1 arcsec oRA Right Ascension offset (1)
13- 17 F5.1 arcsec oDE Declination offset (1)
19- 24 F6.1 Jy S [1.5/1573] Peak flux at 22GHz
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Note (1): Position offsets relative to 05:35:14.3-05:22:33.7 (J2000).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 09-Dec-2014