A new study of an old sink of sulphur in hot molecular cores: The sulphur residue

Abstract

Sulphur appears to be depleted by an order of magnitude or more from its elemental abundance in star-forming regions. In the last few years, numerous observations and experiments have been performed in order to understand the reasons behind this depletion without providing a satisfactory explanation of the sulphur chemistry towards high-mass star-forming cores. Several sulphur-bearing molecules have been observed in these regions, and yet none are abundant enough to make up the gas-phase deficit. Where, then, does this hidden sulphur reside? This paper represents a step forward in our understanding of the interactions among the various S-bearing species. We have incorporated recent experimental and theoretical data into a chemical model of a hot molecular core in order to see whether they give any indication of the identity of the sulphur sink in these dense regions. Despite our model producing reasonable agreement with both solid-phase and gas-phase abundances of many sulphur-bearing species, we find that the sulphur residue detected in recent experiments takes up only ~ 6 per cent of the available sulphur in our simulations, rather than dominating the sulphur budget.