2006ApJ...644L..41C

We present new observations of the Cep A East region of massive star formation and describe an extended and dynamically distinct feature not previously recognized. This feature is present in emission from H₂CS, OCS, CH₃OH, and HDO at -5.5 km/s but is not traced by the conventional tracers of star-forming regions, H₂S, SO₂, SO, and CS. The feature is extended up to at least 0.1 pc. We show that the feature is neither a hot core nor a shocked outflow. However, the chemistry of the feature is consistent with predictions from a model of an eroding interface between a fast wind and a dense core; mixing between the two media occurs in the interface on a timescale of 10-50 yr. If these observations are confirmed by detailed maps and by detections in species also predicted to be abundant (e.g., HCO⁺, H₂CO, and NH₃), this feature would be the first detection of such an interface in regions of massive star formation. An important implication of the model is that a significant reservoir of sulfur in grain mantles is required to be in the form of OCS.