Sulphur-bearing Species in the Star-Forming Region L1689N
Abstract
We report observations of the main S-bearing species, SO, SO2 and H2S, in the low-mass star forming region L1689N. We obtained large scale (∼300''x200'') maps of several transitions from these molecules to study the sulphur chemistry in the region and how the relative abundances change in the different physical conditions found in L1689N. We identified six interesting regions to carry out a quantitative comparative study: the molecular cloud (reference position), four shocked regions caused by the interaction of the molecular outflows with the cloud, and the low-mass class 0 protostar IRAS16293-2422. In these six positions we carefully computed the gas temperature and density by means of a non-LTE code. Then we computed the column density of SO, SO2 and H2S, together with SiO and H2CO which were observed previously, and derived the relevant abundance ratios.
Our first result is that unlike SiO, the observed sulphur species are not a clear signature of shocks. Indeed H2S is not detected and SO2 is slightly enhanced in the shocked regions, whereas the low lying SO lines are dominated by the emission from the molecular cloud. H2CO seems to be correlated with SO2, as they are enhanced in the same regions. The situation is different towards the protostar where SO and SO2 abundances increase by a factor 100 and 300 respectively in the hot core of IRAS16293-2422. The observed H2S, SO and SO2 abundance ratios agree remarkably well with previous theoretical predictions of time dependent chemical models, giving an estimate for the age of IRAS16293-2422 of ∼3 times 104 yr. Finally, we discuss the sulphur budget in the clouds and find that sulphur is mostly depleted into the volatile grain mantles. We also find some evidence that about half of the elemental sulphur is in a form other than H2S, SO and SO2 and we suggest that atomic sulphur as a candidate.- Publication:
-
SFChem 2002: Chemistry as a Diagnostic of Star Formation
- Pub Date:
- 2003
- Bibcode:
- 2003cdsf.conf..445W