DIGIT survey of far-infrared lines from protoplanetary discs: II. CO

Co is an important component of a protoplanetary disc as it is one of the most abundant gas phase species. Furthermore, observations of CO transitions can be used as a diagnostic of the gas, tracing conditions in both the inner and outer disc. CO is not detected in our flat discs as the emission is below the detection limit. We find that HAEBE sources with CO detections have high L[subUV] and strong PAH emission, which is again connected to the heating of the gas. In TTS, the objects with CO detections are all sources with evidence of a disc wind or outflow. For both groups of objects, sources with CO detections generally have high UV luminosity, but this is not a sufficient condition for the detection of the far-IR CO lines.