Sulphur-bearing species in the star forming region L1689N
Résumé
We report observations of the expected main S-bearingspecies (SO, SO2 and H2S) in the low-mass star forming regionL1689N. We obtained large scale (~300''x200'') maps ofseveral transitions from these molecules with the goal to study thesulphur chemistry, i.e. how the relative abundances change in thedifferent physical conditions found in L1689N. We identified eightinteresting regions, where we carried out a quantitative comparativestudy: the molecular cloud (as reference position), five shockedregions caused by the interaction of the molecular outflows with thecloud, and the two protostars IRAS16293-2422 and 16293E. In thecloud we carefully computed the gas temperature and density by meansof a non-LTE LVG code, while in other regions we used previousresults. We hence derived the column density of SO, SO2 andH2S, together with SiO and H2CO - which were observed previously- and their relevant abundance ratios. We find that SiO is themolecule that shows the largest abundance variations in the shockedregions, whereas S-bearing molecules show more moderate variations.Remarkably, the region of the brightest SiO emission in L1689Nis undetected in SO2, H2S andH2CO and only marginally detected in SO. In the other weaker SiOshocks, SO2 is enhanced with respect to SO. We propose a schema inwhich the different molecular ratios correspond to different ages ofthe shocks. Finally, we find that SO, SO2 and H2S havesignificant abundance jumps in the inner hot core of IRAS16293-2422and discuss the implications of the measured abundances.
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