Deuterium chemistry of dense gas in the vicinity of low-mass and massive star forming regions

TL;DR

This study models the deuterium chemistry in dense gas around star forming regions, revealing how factors like depletion efficiency and core density influence deuterium fractionation, and suggesting deuterated sulfur species as evolutionary indicators.

Contribution

It provides a comparative analysis of deuterium chemistry in hot cores and hot corinos, highlighting the impact of physical parameters on deuterium fractionation and proposing new chemical evolutionary markers.

Findings

Depletion efficiency significantly affects deuterium chemistry.

Chemistry is more sensitive to final core density in hot cores.

Deuterated sulfur species ratios serve as evolutionary indicators.

Abstract

The standard interstellar ratio of deuterium to hydrogen (D/H) atoms is $\sim 1.5 \times 10^{-5}$. However, the deuterium fractionation is in fact found to be enhanced, to different degrees, in cold, dark cores, hot cores around massive star forming regions, lukewarm cores, and warm cores ({\it hereafter}, hot corinos) around low-mass star forming regions. In this paper, we investigate the overall differences in the deuterium chemistry between hot cores and hot corinos. We have modelled the chemistry of dense gas around low-mass and massive star forming regions using a gas-grain chemical model. We investigate the influence of varying the core density, the depletion efficiency of gaseous species on to dust grains, the collapse mode and the final mass of the protostar on the chemical evolution of star forming regions. We find that the deuterium chemistry is, in general, most sensitive to variations of the depletion efficiency on to grain surfaces, in agreement with observations. In addition, the results showed that the chemistry is more sensitive to changes in the final density of the collapsing core in hot cores than in hot corinos. Finally, we find that ratios of deuterated sulphur bearing species in dense gas around hot cores and corinos may be good evolutionary indicators in a similar way as their non deuterated counterparts.