Abstract
We present a detailed study of the gas depletion in L183 (= L134N) for a set of important species, namely, CO, CS, SO, N2 H+ 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 ~3 104 cm-3 , while N2 H+ and NH3 seem to deplete at densities close to 106 cm-3 . The latter result is consistent with the Bergin & Langer ([CITE], ApJ, 486, 316) polar (H2 O) ice case but not with the more recent models of Aikawa et al. ([CITE], ApJ, 593, 906). CS depletion occurs much below its (J :2–1) critical density, (7 105 cm-3 ) and therefore makes this species unsuitable to study the density structure of many dark cloud cores.
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