Volume 399, Number 3, March I 2003
|Page(s)||1047 - 1061|
|Section||Interstellar and circumstellar matter|
|Published online||14 February 2003|
Gas-phase CO, CH, and HCN toward Orion-KL*
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, email@example.com
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
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.