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L'oxygene dans le milieu interstellaire: l'apport des donnees spectroscopiques ISO/LWS

Abstract : Oxygen is the most abundant element after Hydrogen and Helium in the Universe. It is therefore of prime importance to know in which form Oxygen is found in the different phases of the interstellar medium (ISM). The constraints imposed by SWAS and ISO observations represent a challenge for theorists as they are in contradiction with the current models. In which form is the Oxygen in molecular clouds and what are the main Oxygen bearing species ? The gas in cold molecular clouds is mainly cooled by atomic Oxygen through its lines in the infrared. First, the tools used during my research are presented, notably the LWS instrument on board the Infrared Space Observatory (ISO). This instrument allowed the observation of the lines of the Oxygen in atomic form. Observations towards star forming regions (HII regions) far from the sun are then presented. The far ultraviolet radiation field emitted by the massive stars illuminates and photo-dissociates the surrounding gas, creating a photo-dissociation region (PDR). The infrared atomic lines of Oxygen ([OI] 63 microns and [OI] 145 microns) and of ionised Carbon ([CII], 158 microns) dominate the gas cooling in these regions. Absorption of the strong continuum emitted by bright sources in some of the observed lines of sight can trace the molecular and diffuse clouds which lie in the galactic spiral arms. The fit of the observed spectra towards two particular HII regions, W49N and Sagittarius B2, allow to characterise both the emitting PDR and the molecular clouds along the lines of sight. This work shows that most of the Oxygen in the gas phase is in atomic form in the molecular clouds. This result is in contradiction with the theoretical works, but these observations agree with the SWAS ones showing that the abundance of the O2 molecule is much less than predicted by the models. These results will help to better constrain the theoretical works to come.
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Contributor : Charlotte Vastel <>
Submitted on : Tuesday, December 10, 2002 - 2:09:08 AM
Last modification on : Thursday, October 15, 2020 - 4:07:08 AM
Long-term archiving on: : Tuesday, September 11, 2012 - 6:55:10 PM


  • HAL Id : tel-00002100, version 1



Charlotte Vastel. L'oxygene dans le milieu interstellaire: l'apport des donnees spectroscopiques ISO/LWS. Astrophysique [astro-ph]. Université Paul Sabatier - Toulouse III, 2001. Français. ⟨tel-00002100⟩



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