SCIENTIFIC ABSTRACT
The main objective of the LWS proposals on Pre-Main Sequence evolution 
is the understanding of the matter evolution from the molecular clouds 
to the compact, hot stellar state of the main sequence stars. The present
proposal deals with the study of the peculiar phase during which powerful,
collimated bipolar outflows are originated from the central object.

A consistent picture of the early phases of stellar evolution has to 
include the understanding of the outflow phenomena and its relationship 
to the central exciting source and its circumstellar disk. 
It has been realized that in order to understand the young stars 
we have to understand their circumstellar disks as these contribute
significantly to the evolution and the energy output from these objects. 
In particular it has been enpirically estabished that the physics 
of these disks is intimately related to the physics of the stellar mass 
loss and possibly to the physics of the mass accretion as well.

The LWS will be used to study the ionization and excitation state of the warm
outflowing gas, to determine the velocity law by comparing the 
observed line intensities with models and mapping the dust opacity in 
the circumstellar disks measuring the line profiles as a function of the
wavelength.

Both spectrometers will be used in low resolution mode, in order to detect
the various spectral features expected to trace the different physical
conditions. We expect to detect line emission from various ionic and molecular
species (in particular H_2O, OI, CO, NII that are among the major coolants in th
e expected physical conditions). 

OBSERVATION SUMMARY
Full spectral scans using the LWS in grating mode are planned for all our
targets. The "on source" integration time for LWS Grating spectra are  
computed in order to observe with S/N=10 lines of 2 10^-20 W/cm^2. For the 
brightest sources this limit is reduced in order to observe with  S/N=10
lines that are 1/200 of their 60 um continuum.

In presence of an "outflow" the "off source" observation is done carrying  
out a map (in "raster scan") of the flow with a full grating spectrum in 
each point of the map. The total integration time spent on all the  points 
of the map will be similar to the one spent on the single  "on source" point;
the reference "off source" point will be therefore  built by binning 
together all the points of the map. 

A full SWS grating scan is foreseen for all the objects  (with the exception 
of the objects  that will be observed in the SWS guaranteed time) with a
25 um IRAS flux sufficient to give S/N=10 on a line that is 1/30 of the
continuum in the SWSO1 mode.
We also scan with SWS01 mode those points in the flow where evidence of
near-infrared shock excited emission exists.