The following document lists the file abstract/CCECCARE_YSO_LINE.abs
from catalogue VI/111.
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We propose to study the physical conditions of the gas in the innermost region of the collapsing envelopes surrounding Young Stellar Objects. In preparation of the ISO mission, we developed a theoretical model (Ceccarelli, Hollenbach and Tielens, 1994) for the predictions of the far infrared line spectrum from a collapsing envelope onto a central object: the model predicts that many water lines and the OI(63um) will be easily detectable by the ISO spectrometers, while CO lines are weaker. Through a careful study of the brightest lines, we selected seven lines (five water lines, OI(63um) line and one CO line) which probethe temperature and density of the gas across the envelope. Moreover, observations of these lines allow to give a direct measure of the water abundance, the mass accretion rate and the presence of a hot component due to a hot circumstellar disk. The three lines in the SWS range come from regions whose infalling velocity can be resolved by the Fabry-Perot. The remaining four lines in the LWS range lie on such strong continua that high resolution observations are needed to detect them. We hence request the SWS07 and LWS04 modes to observe the proposed lines. We notice that water lines are only observable from a space borne platform and ISO provides unique opportunity to detect them. Finally comparison of the predicted line emission from the infalling envelope (our model) with the model by Neufeld and Melnick (1987), that describes water emission from shocked gas (outflow), shows that the two regimes are easily distinguishable.