The following document lists the file abstract/PWESSELI_COMPYSO.abs
from catalogue VI/111.
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Young stellar objects are usually divided in several classes according to the wavelength at which their energy distribution peaks, roughly corresponding to their age. The transition of these stars from a system in which the strongly accreting central pre-main sequence star is heavily embedded in its natal cloud to a system in which most of this cloud has been accumulated into a circumstellar disk and the accretion on the central object has diminished by several orders of magnitude is particularly interesting, since current theories predict that this is the onset of planet formation in these disks. It is expected that the study of the physical phenomena occurring during the different phases can provide us with valuable new insights in this process, which, in the case of the solar system, eventually lead to the formation of inhabitable planets. Intermediate-mass pre-main sequence stars, recognizable as Herbig Ae/Be systems, play a crucial role in these studies, since the evolution of their disks can be followed up to later ages due to their greater luminosity than the low-mass T Tauri stars. Here we ask for discretionary time to complete our ISO study of the transition of intermediate-mass YSO's from the phase at which they start clearing most of their natal cloud to their appearance as Herbig Ae/Be stars surrounded by protoplanetary disks. The goal of these new observations is twofold: (1) investigate the connection between solid-state and gas-phase phenomena in a small number of young objects in which we have found evidence for strong outflow activity, (2) detect the cool molecular hydrogen from the circumstellar disk in a small number of more evolved objects. The combination of these new spectra with our data on these objects from the central program PWESSELI.YSOAEBE proposal will give considerable enhanced value to these spectra and form a unique data-set of immense value for the study of star formation for years to come.