the planets, but until that time, studying the precursors of the planetary systems 

 and using them as analogs for understanding our own solar nebula may help us 

 to assess the potential for life sites elsewhere in the universe. 



During the collapse phase, the opacity in the collapsing envelope is very high 

 in the visible and near-infrared. Essentially, one can hope to see the central 

 object and the dusty disk only in the far-infrared and submillimeter. Fortu- 

 nately, many molecules, atoms, and ions have transitions in these wavelength 

 regions. Poor atmospheric transmission in these wavelength regions mandates 

 observations from Earth orbit. The LDR will be a good instrument for the study 

 of the collapse phase of star formation. The LDR, with a 20-m aperture, can 

 achieve a resolution at 100 micrometers of about 100 AU for protostars in 

 the Taurus cloud, sufficient to resolve the collapsing envelope. Studies of molec- 

 ular rotational transitions can then yield important chemical, spatial, and kine- 

 matic information on the collapsing envelope and the interaction of the outflow 

 with the circumstellar envelope. High spectral resolution (X/AX = 10 s ) is 

 required for such studies. Such high resolution is also required to provide veloc- 

 ity discrimination across the accretion shock on different parts of the proto- 

 planetary disk and on the central object, as well as to study the interaction of 

 the outflow with the circumstellar disk and with the parent molecular cloud. 

 Important lines for these studies are the far-infrared, fine-structure transitions of 

 CM, Ol, and Olll, the high-lying rotational transitions of CO, and the rotational 

 transitions of HD and H 2 . 



Important information on the kinematical structure of the collapsing enve- 

 lope and the outflow, and their interaction, can also be obtained from near- 

 infrared absorption-line studies. Molecular vibrational transitions are particularly 

 useful, because the detailed rotational structure can be used to derive excitation 

 temperatures and total column densities. This may aid in relating potential 

 multiple components spatially. Such studies have already been performed for the 

 luminous, massive protostar in Orion. With a cooled telescope from Earth orbit 

 (e.g., SI RTF and ISO) this also will become possible for less-luminous, less- 

 massive protostars, such as T Tauri stars. High spectral resolution (X/AX = 1 5 ) is 

 imperative to resolve the rotational structure. 



The HST may provide an excellent platform to observe protostars during the 

 latter phases of the collapse, when the envelope has been dispersed by the strong 

 stellar wind. Its high spatial resolution and good ultraviolet sensitivity will allow 

 studies of HH objects and jets much closer to the photospheric surface than 

 presently possible. The ultraviolet lines of high ionization stages of C and O are 

 useful diagnostics for the shock conditions (e.g., pre-shock density, shock veloc- 

 ity). The 0.1-arcsec resolution of the WF/PC on the HST corresponds to about 

 1 AU at the distance of the Taurus cloud. This is probably still insufficient for 

 spatial resolution of the actual acceleration zone of the stellar wind, yet the 

 question of precisely where HH objects originate may be amenable to study 

 from the HST. By imaging through narrow-band filters that isolate specific 



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