Physical conditions in the interstellar and circumstellar medium from ISO observations

We present our results concerning the determination of physical conditions in interstellar and circumstellar clouds. All the data presented here have been obtained with the instruments on board the ISO1 satellite. A raster map of the 179.5 mu m line of H2O centered on SgrB2 has been made with the LWS grating spectrometer shows this line in absorption against the far-infrared continnum at all observed positions with a line absorption depth of approximate to 15%. Fabry-Perot observations of the H2O lines indicate a broad absorption profile between -150 and 100 kms(-1) proving that water vapour is present in the molecular gas along the line of sight toward SgrB2. We derive a lower limit to the H2O abundance in SgrB2 of 10(-5). In Orion-IRC2 we have detected several rotational transitions of water vapour in emission. Transitions involving energy levels higher than 1000 K have been detected Many lines of (H2O)-O-18 and (H2O)-O-17 have also been observed in this source where first estimations indicate a water vapour abundance similar to that of SgrB2. We also report the detection of triatomic carbon in the diffuse interstellar medium through the observation of several re-vibrational lines of its low energy bending mode. Concerning star forming regions we have made a detailed study of the Trifid nebula using the ISOCAM, ISOPHOT, LWS and SWS instruments together with molecular observations from ground based telescopes. A second generation of newly-born stars has been found in the interface between the HII region and surrounding molecular cloud. Finally we present LWS observations and modelling of evolved stars.