Issue |
A&A
Volume 386, Number 3, May II 2002
|
|
---|---|---|
Page(s) | 1074 - 1102 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20020362 | |
Published online | 15 May 2002 |
CO and H2O vibrational emission toward Orion Peak 1 and Peak 2
1
CSIC, IEM, Dpto. Física Molecular, Serrano 123, 28006 Madrid, Spain
2
Universidad de Alcalá de Henares, Departamento de Física, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
3
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
4
School of Physics, University College, Australian Defence Force Academy, University of New South Wales, Canberra ACT 2600, Australia
5
Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85741 Garching, Germany
Corresponding author: E. González-Alfonso, gonzalez@isis.iem.csic.es
Received:
4
December
2001
Accepted:
4
March
2002
ISO/SWS observations of Orion Peak 1 and Peak 2 show strong emission in the
ro-vibrational lines of CO at 4.45–4.95 μm and of H2O
at 6.3–7.0 μm. Toward Peak 1 the total flux in both
bands is, assuming isotropic emission, ≈2.4 and ≈0.53 ,
respectively. This corresponds to ≈14 and ≈3% of the
total luminosity in the same beam. Two temperature components are
found to contribute to the CO emission from Peak 1/2: a
warm component, with
–400 K, and a hot component with
K. At Peak 2 the CO flux from the
warm component is similar to that observed at Peak 1, but the hot
component is a factor of ≈2 weaker.
The band is ≈25% stronger toward Peak 2,
and seems to arise only in the warm component.
The P-branch emission of both bands from the warm component is
significantly stronger than the R-branch, indicating that the
line emission is optically thick.
Neither thermal collisions with nor with H I seem capable of explaining
the strong emission from the warm component. Although the emission arises
in the postshock gas, radiation from the most prominent mid-infrared
sources in Orion BN/KL is most likely pumping the excited vibrational
states of CO and . CO column densities along the line of sight
of
–
are required to explain the band shape,
the flux, and the , and beam-filling is invoked to reconcile this high
N(CO) with the upper limit inferred from the emission. CO is
more abundant than by a factor of at least 2. The density of the
warm component is estimated from the emission to be
~
.
The CO emission from the hot component is neither satisfactorily explained
in terms of non-thermal (streaming) collisions, nor by
resonant scattering. Vibrational excitation through collisions with for
densities of ~
or, alternatively, with atomic hydrogen,
with a density of at least
, are invoked to explain
simultaneously the emission from the hot component and that from the high
excitation lines in the same beam.
A jump shock is most probably responsible for this emission.
The emission from the warm component could in principle be explained
in terms of a C-shock. The underabundance of relative
to CO could be the consequence of photodissociation, but may also
indicate some contribution from a jump shock to the CO warm emission.
Key words: shock waves / ISM: abundances / ISM: individual objects: Orion
© ESO, 2002
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