L183 (L134N) revisited. III. The gas depletion

International audienceWe present a detailed study of the gas depletion in L183 (= L134N) for a set of important species, namely, CO, CS, SO, N_2H+ and NH_3. 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 N_2H+b and NH_3 seem to deplete at densities close to 106 cm-3. The latter result is consistent with the Bergin & Langer (\cite{Bergin97}, ApJ, 486, 316) polar (H_2O) ice case but not with the more recent models of Aikawa et al. (\cite{Aikawa03}, ApJ, 593, 906). CS depletion occurs much below its (J:2-1)b critical density, (7 × 105 cm-3) and therefore makes this species unsuitable to study the density structure of many dark cloud cores. Based on observations made with the CFHT, the Iram 30-m and the ARO 12-m (formerly NRAO 12-m). Appendix A is only available in electronic form at http://www.edpsciences.or