Strip scans with the LWS through the rho Ophiuchi main cloud (L 1688)
are proposed. Full grating scans at high S/N will simultaneously provide
information on the physical state of the gas (spectral lines) and of the
dust particles (continuum/solid state features) in each observed
position. A wide range of excitation conditions are known to exist
within the cloud, as seen in the extended emission of ionic fine
structure transitions, e.g. [C II]158 micron, and in that of low lying
molecular rotational transitions such as CS (J=2-1). What regards the
dust, several cold clumps, immersed in a warmer medium, have been
observed in the submm/mm regime from the ground. In a recent study we
have found that the gas and the dust appear not to be well mixed on
scales of the order of 0.15 pc and the proposed LWS observations will
directly address this issue.

The proposed strip scans will map the major star forming condensations
found in the rho Oph core. Apparently, bodies of substellar mass (`brown
dwarfs') are found near only two of them. In addition, an apparently
inactive condensation will be observed. Combined with the results from
the ISOCAM and ISOPHOT Guaranteed and Open Time surveys for the stellar
population of the cloud, these spectroscopic observations will map the
physics of stellar formation at the relevant frequencies in
unprecedented detail.