Outflow interaction in the late stages of star formation

We have mapped the CO, HCO+, N2H+, and CS emission around a nearby T Tauri star, IRAS 16316-1540. A molecular outflow is seen in CO, HCO+, N2H+, and CS emission originating from the IRAS source, while an envelope is seen in N2H+ and HCO+ emission surrounding the IRAS source. The molecular outflow is bipolar with a southeastern (SE) lobe and a northwestern ( NW) lobe. The structure and the kinematics of the SE lobe are well defined and can be explained with a simple kinematic model. In this model, the SE lobe is a U-shaped shell consisting of a wide-opening base mimicking the reflection nebula RNO 91 and a cylindrical shell with a constant radius mimicking the CO outflow shell. The wide-opening base is expanding toward the circumstellar envelope, while the cylindrical shell is expanding mainly laterally into the ambient medium. If the base of the SE lobe continues to expand at its current velocity, it will meet with the base of the NW lobe and disperse the circumstellar envelope in a few times 10(4) yr. The circumstellar envelope is elongated perpendicular to the outflow axis, extending to the northeast and southwest of the IRAS source. The envelope has differential rotation with the velocity increasing toward the source. It may result from material infalling toward the source carrying its angular momentum. The HCO+ emission near the source may arise from an unresolved inner ring of the envelope, showing two peaks with one on each side of the IRAS source and a position-velocity structure consistent with the rotation law derived from the N2H+ emission. The HCO+ emission in the outer part of the envelope likely traces the swept up envelope material, showing both the outflow motion and probably rotation.