HCO⁺ emission excess in bipolar outflows

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, which 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, which 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.