CO line emission in pre-main sequence sources

We present some overall results, obtained with the Long Wavelength Spectrometer aboard the Infrared Space Observatory (ISO-LWS), of the far-infrared spectra (45-190 μm) of the sources belonging to the pre-main sequence stellar evolution guaranteed time program. Strong molecular lines were detected in most of the Class 0, in the low luminosity Class I and in some Class II sources: for the first time thermally excited water was observed, plus several hydroxl lines and carbon monoxide high-J transitions. All these lines can be explained by the presence of a warm and dense (T=200 - 2000 K; n(H2)=104-106 cm-3) gas component