Issue |
A&A
Volume 399, Number 3, March I 2003
|
|
---|---|---|
Page(s) | 1047 - 1061 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20021799 | |
Published online | 14 February 2003 |
Gas-phase CO
, C
H
, and HCN toward Orion-KL*
1
Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
2
SRON National Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
3
Department of Physics and Astronomy, Denison University, Granville, Ohio 43023, USA
4
School of Physics, University College, ADFA, UNSW, Canberra ACT 2600, Australia
5
Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85741 Garching, Germany
Corresponding author: A. M. S. Boonman, boonman@strw.leidenuniv.nl
Received:
10
June
2002
Accepted:
22
November
2002
The infrared spectra toward Orion-IRc2, Peak 1 and Peak 2 in the 13.5–15.5 μm wavelength range are presented, obtained with the Short
Wavelength Spectrometer on board the Infrared Space Observatory.
The spectra show absorption and emission features of the
vibration-rotation bands of gas-phase
CO2, HCN, and C2H2, respectively. Toward the deeply embedded massive
young stellar object IRc2 all three bands appear in
absorption, while toward the shocked region Peak
2 CO2, HCN, and C2H2 are seen in emission. Toward Peak 1 only
CO2 has been detected in emission.
Analysis of these bands shows that the
absorption features toward IRc2 are characterized by excitation
temperatures of ~175–275 K, which can be explained
by an origin in the shocked plateau gas. HCN and C2H2 are only seen
in absorption in the direction of IRc2, whereas
the CO2 absorption is probably
more widespread. The CO2 emission toward Peak 1 and 2
is best explained with excitation by infrared radiation from
dust mixed with the gas in
the warm component of the shock. The similarity of the CO2 emission and
absorption line shapes toward IRc2, Peak 1 and Peak 2 suggests that
the CO2 is located
in the warm component of the shock ( K) toward all three positions.
The CO2 abundances of ~10-8 for Peak 1 and 2, and of a few
times 10-7 toward IRc2 can be explained
by grain mantle evaporation and/or reformation in the gas-phase
after destruction by the shock.
The HCN and C2H2 emission detected toward Peak 2 is narrower
(
–150 K) and originates either
in the warm component of the shock or in the extended ridge.
In the case of an origin in the warm component of the shock, the low HCN and
C2H2 abundances of ~10-9
suggest that they are destroyed by the shock or have
only been in the warm gas for a short time (
yr).
In the case of an origin in the extended ridge, the inferred abundances
are much higher and do not agree with predictions from current chemical
models at low temperatures.
Key words: stars: formation / ISM: individual objects: Orion IRc2, Peak 1, Peak 2 / ISM: abundances / ISM: molecules / ISM: lines and bands / molecular processes
© ESO, 2003
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