2005A&A...429..181P

We present a detailed study of the gas depletion in L183 (= L134N) for a set of important species, namely, CO, CS, SO, N₂H⁺and NH₃. We show that all these species are depleted at some level. This level seems to depend mostly on a density threshold rather than on dust opacity. Therefore UV shielding would not be a main factor in the triggering of depletion. Our data suggest that CO, CS and SO depletion happen at densities of ∼3x10⁴cm^–3, while N₂H⁺and NH₃ seem to deplete at densities close to 10⁶/cm3. The latter result is consistent with the Bergin & Langer (1997ApJ...486..316B) polar (H₂O) ice case but not with the more recent models of Aikawa et al. (2003ApJ...593..906A). CS depletion occurs much below its (J:2-1) critical density, (7x10⁵cm^–3) and therefore makes this species unsuitable to study the density structure of many dark cloud cores.