1999A&A...346..278H

Many protostellar outflows show high velocity molecular bullets, in addition to a low velocity molecular outflow and shocked H₂ knots. The velocities of these bullets suggets that they are closely related to the protostellar wind. We demonstrate from ¹²CO 4-3 and lower-J ¹²CO and ¹³CO observations that the CO bullets are hot, as expected for actively shocked molecular material. This upwardly revised temperature estimate implies that the bullets are more massive than was previously considered. The high masses have consequences for models of the origin of the bullets. They cannot consist of locally swept up material; they can form of material swept up along their path only if that path is much longer than the distance between the bullets; alternatively, if they consist of jet material then the jet must have a density of ∼10⁴cm^–3.