2010ApJ...722.1633S

The distributions of CCH, C₄H, c-C₃H₂, and HC₅ N have been studied in high spatial resolution with the Plateau de Bure Interferometer, where the short-spacing data have been taken with the IRAM 30 m telescope. The distributions show clear central condensation around the protostar, confirming that these molecules are associated with the protostar's environment. The blueshifted and redshifted components are concentrated near the protostar, indicating their existence in the infalling envelope. The intensity distribution of c-C₃H₂ shows a steep increase inward of a radius of 500-1000 AU from the protostar. By comparing the c-C₃H₂ distribution with the H₂column density distribution from the protostellar envelope model using the DUSTY code, the abundance of c-C₃H₂ is found to be enhanced by a factor of about 10 within the increasing point, where the temperature becomes higher than 20-30 K. This result supports the picture of warm carbon-chain chemistry; carbon-chain molecules and their related molecules are efficiently regenerated by evaporation of CH₄ from dust grains in the warm region (about 25 K). The distributions of CCH and C₄ H have extended structures as well as an enhanced component, which implies a contribution of "remnant" carbon-chain molecules produced in the starless-core phase in addition to the regeneration component. On the other hand, the distributions of CCH, C₄H, and c-C₃H₂ have a slight dip with a radius of 300-600 AU toward the protostar position, indicating that their abundances would decrease toward the central part. The present results provide a new picture of carbon-chain chemistry in the closest vicinity of a low-mass protostar.