Molecular abundances in low-mass protostellar envelopes
  A study of the chemical structure of the envelopes around a sample protostars is introduced. Physical models for the envelopes derived using 1D radiative transfer modeling of their dust continuum emission are used as input for Monte Carlo modeling of single-dish line observations in order to establish the chemical inventories for the different sources. CO and HCO+ abundances are found to be correlated with envelope mass: the sources with the most massive envelopes show the lowest abundances, supporting the idea that the depletion of these molecules is most efficient in the colder, denser environments. Other molecules like CS and HCN do not show a similar trend. Deuterated species like DCO+ and DCN also show signs of correlations with envelope mass and temperature: the deuterium fractionation of HCO+ is most prominent for the coldest and most massive envelopes in the sample and at the same time anti-correlated with the fractionation of HCN. This puts constraints on the low temperature gas-phase deuterium chemistry. 
Jes K. Jorgensen, Fredrik L. Schoeier and Ewine F. van Dishoeck   (Leiden Observatory)