A plausible model is proposed for the enhancement of the abundance of
molecular species in bipolar outflow sources. In this model, levels of HCO+
enhancement are considered based on previous chemical calculations, that are
assumed to result from shock-induced desorption and photoprocessing of dust
grain ice mantles in the boundary layer between the outflow jet and the
surrounding envelope. A radiative transfer simulation that incorporates
chemical variations within the flow shows that the proposed abundance
enhancements in the boundary layer are capable of reproducing the observed
characteristics of the outflow seen in HCO+ emission in the star forming core
L1527. The radiative transfer simulation also shows that the emission lines
from the enhanced molecular species that trace the boundary layer of the
outflow exhibit complex line profiles indicating that detailed spatial maps of
the line profiles are essential in any attempt to identify the kinematics of
potential infall/outflow sources. This study is one of the first applications
of a full three dimensional radiative transfer code which incorporates chemical
variations within the source.Comment: MNRAS, accepted. 10 pages, 6 figure